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ELEMENTARY   PLANT   BIOLOGY 


THE  MACMILLAN  COMPANY 

NEW  YORK    .    BOSTON  •    CHICAGO 
DALLAS   •    SAN   FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON   •   BOMBAY  .    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 
TORONTO 


•^/^^:iS!@^ 


I 

- 


View  in  the  Hemlock  Forest,  New  York  Botanical  Garden.  —  (Courtesy 
of  New  York  Botanical  Garden.) 


ELEMENTARY  PLANT  BIOLOGY 


BY 


JAMES   EDWARD   PEABODY,   A.M. 

1 1 

HEAD   OF   THE    DEPARTMENT    OP    BIOLOGY,    MORRIS    HIGH    SCHOOL 
BRONX,    NEW    YORK    CITY,    AUTHOR    OF    "STUDIES    IN    PHYSI- 
OLOGY "    AND    "  LABORATORY    EXERCISES    IN    ANATOMY 
AND   PHYSIOLOGY  " 

AND 

ARTHUR   ELLSWORTH   HUNT,  Pn.B. 

HEAD    OF    THE    DEPARTMENT    OF    BIOLOGY,    MANUAL    TRAINING 
HIGH   SCHOOL,    BROOKLYN,    NEW   YORK   CITY 


gorfe 

THE   MACMILLAN   COMPANY 
1912 

All  rights  reserved 


BIOLOGY 

LIBRARY 

G 


COPYRIGHT,  1912, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.    Published  February,  1912. 


Nortooorj 

J.  8.  Cushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


TO 
THE  MEMORY  OF 

MARTHA  FREEMAN  GODDARD 

WHOSE    DEVOTED    INSTRUCTION    IN    BIOLOGY   IS    A    LASTING 

INFLUENCE    FOR    GOOD    IN   THE    LIVES  OF    HUNDREDS 

OF    BOYS     AND    GIRLS    AND     WHOSE     RARE     SKILL 

IN     LEADERSHIP     IS     AN    INSPIRATION     TO 

EVERY    TEACHER    WHO    KNEW    HER 

THIS  BOOK  IS  DEDICATED 

BY   THE    AUTHORS 


PREFACE 

ALL  the  activities  of  a  plant,  of  an  animal,  or  of  man  may 
be  grouped  in  three  classes.  One  class  embraces  the  func- 
tions relating  to  the  life  of  the  individual  organism.  These 
functions  have  to  do  with  the  processes  of  eating,  digest- 
ing, assimilating,  taking  in  of  oxygen,  producing  of  energy, 
and  excreting  of  waste  matters.  These  may  be  called  the 
nutritive  functions,  if  the  term  is  used  in  its  broadest  sense. 
To  the  second  group  of  activities  belong  the  functions  that 
have  to  do  with  the  perpetuation  of  the  animal  or  plant 
species,  and  these  are  known  as  the  reproductive  functions. 
Living  organisms,  whether  plant,  animal,  or  human,  may,  in 
the  third  place,  be  considered  in  their  relations  to  one  another 
and  especially  to  the  general  welfare  of  mankind.  Thus  we 
may  discuss  the  beneficial  or  injurious  effects,  so  far  as  man 
is  concerned,  of  different  kinds  of  insects  or  of  various  types 
of  bacteria ;  we  may  learn  of  the  activities  of  individual  men 
or  of  groups  of  individuals  which  promote  or  retard  the 
advance  of  human  society ;  or  we  might,  if  we  were  to  carry 
the  study  still  farther,  even  seek  to  learn  the  ways  by  which 
the  higher  thoughts  of  mankind,  as  expressed  in  poetry, 
music,  and  religion,  affect  the  development  of  the  human 
race. 

In  the  preparation  of  this  text,  the  authors  have  sought 
to  keep  continually  in  mind  these  three  classes  of  activities, 
and  to  unify  the  study  of  plant,  animal,  and  human  biology 
by  choosing  those  topics  for  laboratory  work  or  text  descrip- 
tion that  have  to  do  in  a  broad  sense  with  one  or  the  other  of 
the  three  great  groups  of  functions  of  living  things  to  which 

vii 


viii  PREFACE 

we  have  just  referred.  In  doing  this,  they  are  conscious 
that  many  subjects  have  been  slighted  or  altogether  omitted 
which  might  well  be  treated  in  a  year's  work  in  either  botany, 
or  zoology,  or  human  physiology. 

Again,  in  the  treatment  of  a  given  subject,  for  example, 
stems,  fishes,  or  circulation,  special  emphasis  might  be  laid 
on  structure,  on  function,  or  on  the  relation  of  the  given  topic 
to  human  life.  Books  both  interesting  and  scientifically 
worth  while  could  be  prepared  along  any  one  of  these  lines, 
or,  if  time  permitted,  all  three  phases  might  be  equally  em- 
phasized. But  when  we  remember  that  less  than  two  hun- 
dred school  periods  will  probably  be  devoted  by  the  average 
student  to  the  study  of  biology,  the  necessity  for  adhering 
pretty  consistently  to  some  one  plan  is  obvious. 

In  the  judgment  of  the  authors  the  kind  of  biology  most 
worth  while  for  the  average  boy  or  girl  of  fourteen  years 
of  age  is  not  one  based  primarily  on  structure.  Young  stu- 
dents are  naturally  more  interested  in  activities  or  func- 
tions than  they  are  in  mere  form  or  structure.  Hence,  if  we 
wish  to  work  with,  rather  than  "  against  the  grain,"  we  must 
put  function  in  the  foreground  of  our  discussion.  Every  boy 
and  girl  knows,  too,  that  both  plants  and  animals  as  well  as 
human  beings  must  have  food  and  drink,  and  that  they  grow 
and  reproduce  their  kind.  It  is  relatively  much  easier, 
therefore,  to  unify  a  course  like  this  along  physiological  lines 
than  on  the  basis  of  morphology,  or  of  homologies  of  structure, 
many  of  which  are  far  too  complicated  to  be  made  clear  to 
young  students. 

If  properly  outlined  and  presented,  there  is  probably  no 
subject  in  the  school  curriculum  that  can  be  made  of  more 
service  to  a  growing  youth  than  can  biology.  Biological 
problems  confront  him  at  every  turn,  and  if  he  is  a  normal 
being,  he  will  have  asked  himself  question  after  question 


PREFACE  ix 

which  an  elementary  knowledge  of  biology  ought  to  help  him 
to  answer.  Some  of  these  questions  may  be  the  following : 
Whence  comes  the  food  and  oxygen  supply  used  by  man? 
Why  are  food  and  oxygen  needed  in  our  bodies?  Why  are 
some  substances  beneficial  to  the  body  and  others  injurious? 
What  is  the  cause  of  disease,  and  how  is  disease  transmitted? 
And  if  we  were  to  tabulate  the  biological  questions  that  occur 
spontaneously  to  the  average  pupil  in  the  first  year  in  the 
high  school,  we  should  doubtless  find  that  a  great  proportion 
of  these  questions  had  to  do  with  the  relation  of  the  living 
world  to  human  life.  Is  it  not  clear,  therefore,  if  we  are  to 
outline  a  course  in  biology  that  will  best  fit  the  interests  of 
the  "  live  material/'  i.e.  the  boy  or  girl  who  is  to  take  the 
course,  that  the  central  idea  or  factor  must  be  man ;  that  all 
the  various  functions  considered  must  have  some  relation  to 
human  life ;  and  that  the  course,  to  be  of  practical  importance, 
must  suggest  to  the  youth  better  ways  of  carrying  on  his  own 
life  and  of  helping  to  improve  the  surroundings  in  which  he 
lives  ? 

In  order,  however,  to  treat  intelligently  such  a  function,  for 
example,  as  respiration  or  digestion,  it  is  of  course  necessary 
to  know  something  of  the  machinery  by  which  each  of  these 
processes  is  carried  on,  and  so  there  must  be  at  least  a  mini- 
mum consideration  of  the  structure  of  plants,  animals,  and 
the  human  body.  In  every  case,  however,  the  authors  have 
called  attention  only  to  those  details  which  seem  to  be  abso- 
lutely essential  for  an  interpretation  of  the  function  under 
consideration.  Whenever  names  in  common  use  are  suffi- 
ciently accurate  for  descriptions,  these  are  chosen  in  prefer- 
ence to  scientific  terms.  Frequently  the  latter  are  neces- 
sarily used,  and  so,  whenever  their  meaning  is  made  clearer 
by  referring  to  their  derivation  from  Latin  or  Greek,  these 
derivations  are  indicated  in  parentheses. 


X  PREFACE 

The  sections  in  coarse  type  contain  the  material  that  seems 
to  the  authors  most  essential  for  any  clear  understanding  of 
the  subject  as  a  whole,  while  in  fine  type  we  have  put  addi- 
tional laboratory  work  and  text  description  which  we  believe 
to  have  an  important  bearing  on  the  various  topics  discussed. 
If  both  coarse  and  fine  print  on  animal,  or  plant,  or  human 
biology  are  used,  sufficient  material  for  a  half-year  course  in 
either  elementary  botany,  zoology,  or  human  physiology  will 
be  provided. 

In  the  judgment  of  the  authors,  plant  biology  should  always 
be  considered  first  and  human  biology  last  in  the  course  for 
the  following  reasons :  (1)  Plants  lend  themselves  far  more 
readily  to  close  observation  and  especially  to  experiments 
than  do  animals,  and  so  fundamental  processes  which  apply 
to  all  living  things  can  be  demonstrated  scientifically  from 
plant  material.  (2)  Plants  are  the  final  source  of  all  the  food 
supply  of  animals  and  man,  and  if  the  composition  and  manu- 
facture of  the  nutrients  are  taught  early  in  the  course,  a  solid 
foundation  is  laid  for  all  subsequent  study  of  nutrition  in 
animals  and  man.  (3)  The  purpose  of  the  animal  study  is 
largely  that  of  showing  the  adaptations  of  animal  structure 
to  functions  and  the  relations  of  the  animals  studied  to 
human  welfare.  (4)  And  finally,  if  human  biology  comes 
last  in  the  course,  it  may  be  presented  in  such  a  way  as  to 
review,  sum  up,  and  give  real  significance  to  many  of  the 
facts  learned  earlier  in  the  course.  In  fact,  as  the  work 
proceeds,  comparisons  will  constantly  be  made  between 
plants,  animals,  and  man  to  show  that  the  essential  differ- 
ences in  the  three  kinds  of  organisms  consist  not  in  the  dif- 
ferences in  the  functions  which  they  carry  on,  but  in  the 
organs  by  which  the  functions  are  performed. 

So  far  as  the  order  of  individual  topics  under  plant,  ani- 
mal, and  human  biology  is  concerned,  the  instructor  should 


PREFACE  .   xi 

plan  the  sequence  that  best  fits  the  season.  In  fact,  the  last 
use  that  a  good  teacher  will  make  of  any  laboratory  manual 
or  text-book  is  that  of  following  it  slavishly.  It  is  the  hope 
of  the  authors,  however,  that  the  laboratory  guides  and  the 
text  descriptions  which  follow  may  be  sufficiently  sugges- 
tive to  help  some  teachers  to  work  out  improved  methods 
in  biological  instruction.  In  Appendix  II  will  be  found  a 
suggested  order  of  topics  which  the  authors  have  found 
satisfactory. 

Living  organisms  are  to  a  large  extent  to  be  regarded  as 
chemical  engines  so  constructed  as  to  liberate  different  kinds 
of  energy.  No  one,  of  course,  knows  in  any  ultimate  sense 
how  even  the  simplest  functions  are  performed  by  the  sim- 
plest animals  or  plants.  But  it  is  utterly  useless  to  attempt 
to  teach  biological  functions  without  first  presenting  some  of 
the  elementary  principles  involved  in  physical  and  chemical 
phenomena.  For  this  reason  the  first  chapter  in  Plant 
Biology  is  devoted  to  the  study  of  the  Composition  of  Lifeless 
and  Living  Things.  In  Chapter  III  is  a  brief  discussion  of 
the  structure  of  a  common  plant,  and  since  cells  are  funda- 
mentally alike  in  structure  and  functions  in  all  living  or- 
ganisms, emphasis  is  laid  early  in  the  course  on  the  essential 
characteristics  of  these  cellular  elements  in  plants.  Another 
topic  which  necessarily  recurs  throughout  plant,  animal,  and 
human  biology  is  the  principle  of  osmosis  and  its  applica- 
tions. The  authors  have  inserted  experiments  which  in  their 
experience  have  helped  to  fix  in  mind  this  important  principle 
and  which  demonstrate  the  necessity  of  digestion  in  plants 
and  animals. 

After  this  brief  consideration  of  the  fundamentals  of  plant 
composition,  structure,  and  processes,  Chapters  V,  VI,  and 
VII  are  devoted  to  the  study  of  the  adaptations  of  plants 
for  performing  nutritive  and  reproductive  functions.  In 


xii  PREFACE 

Chapter  VIII  are  grouped  experiments  and  descriptions 
the  aim  of  which  is  to  show  various  ways  in  which  plants 
are  propagated.  This  treatment  presents  only  the  briefest 
statement  of  underlying  principles,  since  any  extended  dis- 
cussion of  this  topic  belongs  to  a  course  in  agriculture. 

In  Chapters  IX  (Plants  in  their  Relation  to  Human  Wel- 
fare) and  X  (Plant  Classification)  the  method  of  presentation 
is  strikingly  different  from  that  adopted  in  the  rest  of  the 
book,  particularly  so  in  the  treatment  of  the  spore-bearing 
plants.  The  authors  believe  that  every  pupil  should  be 
taught  something  of  these  simpler  forms  (especially  bacteria), 
and  that  he  should  get  as  many  of  these  facts  as  possible  by 
observation.  But  to  expect  much  laboratory  work  from  young 
students  on  difficult  microscopic  forms  like  many  of  these 
cryptogams,  is,  we  are  confident,  quite  out  of  the  question. 
We  have,  therefore,  frankly  abandoned  the  inductive  method 
of  study  and  have  suggested  that  the  laboratory  work  be 
largely  in  the  nature  of  demonstrations.  It  is,  of  course, 
understood  that  if  these  forms  are  studied,  the  drawings  and 
descriptions  will  be  prepared  from  material  in  the  hands  of 
the  student. 

In  our  judgment  there  are  few  if  any  biological  topics 
which  are  more  important  in  their  practical  bearings  than  is 
that  of  bacteria.  As  commonly  studied  the  disease-pro- 
ducing effects  of  these  organisms  are  emphasized  so  much  that 
boys  and  girls  do  not  appreciate  that  all  the  work  of  the 
higher  plants  depends  ultimately  upon  the  activity  of  these 
low  forms  of  fungi.  In  order  to  bring  out  this  aspect  of  the 
work  of  bacteria  and  for  other  obvious  reasons  the  structure, 
physiology,  and  economic  benefit  of  these  organisms  are  con- 
sidered in  the  chapter  on  the  relation  of  plants  to  human 
welfare,  while  their  pathogenic  effects  are  reserved  for  dis- 
cussion in  human  biology. 


PREFACE  Xlii 

In  the  preparation  of  this  book  the  authors  have  received 
a  great  many  suggestions  from  the  teachers  in  their  own 
departments  and  those  of  other  schools.  Our  thanks  are  due 
to  Miss  M.  Helen  Smith  of  the  Manual  Training  High  School, 
Brooklyn,  N.  Y.  for  several  laboratory  outlines  which  formed 
the  basis  of  corresponding  studies  in  the  following  pages. 
The  authors  have  been  especially  fortunate  in  securing  the 
constructive  criticism  of  Dr.  C.  Stuart  Gager,  Director  of 
the  Brooklyn  Botanic  Garden  of  the  Brooklyn  Institute  of 
Arts  and  Sciences.  He  has  carefully  read  all  of  the  manu- 
script and  the  page  proofs. 

We  are  indebted  to  Dr.  H.  J.  Webber,  Professor  E.  O. 
Fippin,  and  others  at  Cornell  University,  for  valuable  ma-* 
terial  and  illustrations  for  the  chapter  on  Plant  Propagation. 
We  wish,  also,  to  express  our  hearty  appreciation  of  the 
generous  permission  of  Henry  Holt  &  Co.  to  use  some  of  the 
material  published  in  Peabody's  "  Laboratory  Exercises  in 
Anatomy  and  Physiology."  We  are  fortunate,  too,  in  secur- 
ing from  the  New  York  Botanical  Garden  photographs  for 
the  frontispiece,  and  for  several  fine  cuts  in  the  text,  and  from 
Professor  E.  M.  East  of  Harvard  University  the  cut  for  Fig. 
52.  Miss  Mabelle  Baker,  Miss  Clara  Lang,  Miss  Margaret 
Cutler,  and  Miss  Grace  Gamble,  students  in  our  first-year 
classes,  have  kindly  prepared  for  us  the  figures  on  which 
their  several  names  appear. 

Cost  prices  for  the  items  on  the  list  of  laboratory  appara- 
tus and  equipment  were  kindly  furnished  us  by  Bausch  & 
Lumb,  Kny-Scheerer,  and  O.  T.  Louis;  from  these  prices  the 
estimates  on  pp.  173  to  177  were  prepared. 

J.  E.  P. 
A.  E.  H. 

January  31,  1912. 


TABLE   OF   CONTENTS 

PACK 

PREFACE vii 

CHAPTER 

I.     GENERAL  INTRODUCTION 1 

II.     COMPOSITION  OF  LIFELESS  AND  LIVING  THINGS  .        .  5 

I.     Elements,  Compounds,  and  Oxidation         .        .  5 

II.     Definitions .12 

III.     A  Study  of  the  Food  Substances          ...  13 

IV".     Manufacture  of  the  Food  Substances  by  Plants  .  22 

^  III.     THE  GENERAL  STRUCTURE  OF  PLANTS          ...  26 

IV.     OSMOSIS  AND  DIGESTION    • 32 

V.     ADAPTATIONS  OF  THE  NUTRITIVE  ORGANS  OF  PLANTS  39 

I.     The  Structure  and  Adaptations  of  Roots     .         .  39 

II.     The  Structure  and  Adaptations  of  Stems     .         .  45 

III.     The  Structure  and  Adaptations  of  Leaves  .         .  52 

VI.     RESPIRATION  AND   THE   PRODUCTION  OF   ENERGY  IN 

PLANTS 64 

VII.     REPRODUCTION  IN  PLANTS 70 

I.     The  Structure  and  Adaptations  of  Flowers         .  70 

II.     The  Structure  and  Adaptations  of  Fruits    .         .  89 

VIII.    PLANT  PROPAGATION 97 

I.     Seeds  and  their  Development  into  Plants    .         .  97 
II.     (Optional.)     Other  Methods  of  Plant  Propaga- 
tion         .105 

III.  Conditions  Essential  for  the  Growth  of  Plants  .  108 

IV.  (Optional.)     The  Struggle  for  Existence  and  its 

Effects 114 

V.     (Optional.)    The  Improvement  of  Plants  by  Man  119 


xvi  TABLE  OF  CONTENTS 

CHAPTER  PAGE 

IX.     PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE        .  126 

I.     Some  of  the  Uses  of  Plants  to  Man          .        .        .  126 

II.     The  Uses  of  Forests  and  Forest  Conservation          .  132 

III.     Fungi  and  their  Relation  to  Human  Welfare         .  139 

X.    PLANT  CLASSIFICATION 154 

I.     (Optional.)     Common  Methods  of  Classification    .  154 

II.     (Optional.)     Scientific  Methods  of  Classification  .  158 

APPENDIX 

I.     Laboratory  Equipment 171 

II.     Order  of  Topics     .        .        ,        ,        .        .        ..        .  178 

III.  Biology  Note-books       . 181 

IV.  Review  Topics  in  Plant  Biology   .         .         .         .         .  188 
V.     List  of  Suggested  Books  of  Reference  in  Biology         .  197 


ELEMENTARY   PLANT   BIOLOGY 


PLANT  BIOLOGY 

CHAPTER  I 
GENERAL  INTRODUCTION 

1.  Lifeless  Things  and  Living  Things.  —  As  we  look  about 
us,  we  find  that  the  world  in  which  we  live  is  wholly  composed 
of  two  classes  of  things,  which  we  commonly  speak  of  as 
living  things  and  lifeless  things.  Soil,  air,  and  water,  for 
example,  we  know  to  be  lifeless.  Water  is  probably  the 
simplest  of  these  three  so  far  as  its  composition  is  concerned. 
Soil,  on  the  other  hand,  is  very  complex  in  composition,  being 
formed  of  nearly  all  the  substances  known  to  the  scientist. 
Enveloping  the  earth  is  a  mixture  of  gases  called  the  atmos- 
phere which  extends  outward  in  every  direction  for  a  dis- 
tance of  about  fifty  miles.  Everybody  knows,  too,  that  over 
the  surface  of  the  earth,  in  the  water,  and  even  in  the  air 
are  countless  numbers  of  living  things  which  we  designate 
as  either  plants  or  animals. 

One  might  think  that  it  would  be  an  easy  matter  to  set 
down  the  characteristics  by  which  living  things  are  dis- 
tinguished from  those  that  are  lifeless.  And  such  is  the  case 
when  we  compare  a  rock  in  a  field  with  a  horse  that  is  feeding 
beside  it.  Unlike  the  animal,  the  lifeless  rock  is  unable  to 
move  itself,  it  neither  eats  nor  breathes,  and  it  gives  no 
evidence  of  feeling  or  of  will  power. 

But  suppose  we  select  for  comparison  a  railroad  locomotive 
and  a  horse.  Both  move ;  both  need  a  plentiful  supply  of  air ; 


2  PLANT- BIOLOGY 

both  develop  heat  and  power  to  do  work ;  and  both  give  off 
certain  waste  matters.  The  horse,  we  may  say,  requires  food, 
but  so  does  the  engine ;  for  coal  and  water  are  as  necessary 
for  the  development  of  heat  and  power  in  the  engine,  as  food 
and  water  are  for  a  similar  purpose  in  the  horse. 

When  we  try  to  state  characteristics  that  will  distinguish 
all  plants  from  all  lifeless  objects,  we  find  the  task  still  more 
difficult ;  for  most  plants  do  not  move  about  from  place  to 
place,  it  is  difficult  to  realize  that  they  give  off  heat,  and  they 
do  not  give  evidence  that  they  have  conscious  feelings  as 
do  the  common  animals.  In  spite,  however,  of  these  simi- 
larities, we  are  usually  able  to  distinguish  living  from  life- 
less objects  at  least  by  the  three  following  characteristics. 

2.  Growth  of  Living  Things.  —  In  the  first  place  living 
things  use  some  of  the  food  they  eat  for  growth.     No  one  ever 
heard  of  an  engine  or  other  lifeless  object  beginning  as  a  small 
machine,  and  then  slowly  growing  larger  until  it  comes  to 
have  many  times  its  former  weight.1     Yet  this  is  what  hap- 
pens to  all  plants  and  all  animals.     The  average  child,  for 
instance,  at  birth  weighs  seven  to  eight  pounds ;  while  a  man's 
weight  is  over  twenty  times  as  great.     And  if  we  try  to  com- 
pare the  weight  of  an  oak  tree  with  that  of  an  acorn  from 
which  it  started,  the  amount  of  increase  we  find  to  be  enor- 
mous. 

3.  Repair  of  Living  Things.  —  In  the  second  place,  parts 
of  a  locomotive  or  of  any  other  lifeless  machine  by  continual 
use  become  worn  or  broken,  and  the  engine  must  be  sent  to 
the  machine-shop  for  repairs.     Our  bodies,  too,  are  being 
constantly  worn  away ;  for  every  time  we  make  a  motion  of 

*  While  it  is  true  that  icicles  and  other  crystals  apparently  grow, 
this  kind  of  growth  is  brought  about  wholly  by  the  addition  of  mate- 
rial to  the  outer  surface. 


GENERAL    INTRODUCTION  3 

any  sort,  some  of  our  living  muscle  is  used  up ;  every  time 
we  think  or  exert  our  will  power,  some  of  the  living  brain 
substance  is  probably  changed  into  dead  waste  material. 
But  in  contrast  to  lifeless  machines,  our  bodies  are  self-repair- 
ing. The  food  we  eat  not  only  goes  to  increase  the  size  of 
the  body ;  it  also  furnishes  material  to  make  good  the  wear 
and  tear  of  everyday  life.  This  power  of  self-repair  is  like- 
wise present  in  all  animals  and  in  plants  as  well. 

4.  Reproduction  of  Living  Things.  —  A  third   character- 
istic that  distinguishes  living  things  from  those  that  are  life- 
less is  the  fact  that  they  produce  seeds  (in  the  case  of  plants) 
or  eggs  (in  the  case  of  animals),  which  in  turn  come  to  form 
plants  or  animals  like  those  by  which  these  seeds  or  eggs 
were  produced.     No  lifeless  object  can  do  this.     We  shall 
find  in  our  laboratory  study  that,  while  there  are  a  great 
many  different  methods  of  producing  these  new  organisms, 
still  in  their  essential  features  these  various  methods  of  repro- 
duction are  much  the  same  from  the  lowest  plants  to  the 
highest  animals. 

5.  Summary.  —  In  brief,  then,  we  may  say  that  all  liv- 
ing things  have  the  power  of  growth  from  within,  of  self-repair, 
and  of  the  reproduction  of  their  kind;  but  that  so  far  as  we  know 
lifeless  objects  possess  none  of  these  powers. 

6.  Science  and  its  Subdivisions.  —  Ever  since  the  dawn  of 
history  we  find  that  mankind  has  been  seeking  to  learn  the 
secrets  of  living  and  lifeless  matter.     During  the  past  century 
our  knowledge  has  increased  so  rapidly  that  many  sciences 
have  been  completely  rewritten.     The  discoveries,  for  ex- 
ample, of  the  characteristics  of  radium  and  of  X-rays  have 
revolutionized  much  of  what  was  formerly  believed  as  to  the 
properties  of  lifeless  matter.     In  the  same  way  our  increased 
knowledge  regarding  germs  and  other  microscopic  plants  and 


4  PLANT  BIOLOGY 

animals  has  made  possible  the  scientific  treatment  of  disease, 
and  what  is  more  important,  the  prevention  of  disease.  As 
our  knowledge  of  the  living  and  lifeless  world  has  increased, 
it  has  become  necessary  to  divide  this  knowledge  into  a  great 
many  different  branches,  some  of  which  are  physics,  chemis- 
try, geology  (a  study  of  the  earth),  mathematics,  psychology 
(a  study  of  mind),  and  biology. 

7.  Biology  (from  Greek,  bi'os  =  life  +  lo'gos  =  discourse)  is 
the  general  name  given  to  the  study  of  all  living  things. 
Hence,  this  science  treats  of  both  animals  and  plants.  If  we 
confine  our  study  to  the  structure  and  activities  of  plants 
alone,  we  call  this  part  of  the  science  plant  biology,  or  botany. 
Animal  biology,  or  zoology,  on  the  other  hand,  treats  of  ani- 
mals. So-called  human  physiology  (better  known  as  human 
biology)  discusses  man,  the  highest  type  of  the  animal  king- 
dom ;  hence,  it  is  a  branch  of  the  science  of  zoology,  which  in 
turn  is  one  of  the  subdivisions  of  the  study  of  biology. 


CHAPTER  II 
COMPOSITION   OF  LIFELESS   AND  LIVING  THINGS 

8.  Introduction.  —  For  a  great  many  years  scientists 
have  been  studying  plants  and  animals,  and  from  this 
study  they  have  learned  that  the  bodies  of  all  living  organ- 
isms, including  human  beings,  are  made  from  substances 
found  in  the  water,  soil,  and  air,  and  that  when  plants  and 
animals  cease  to  live,  their  bodies  are  changed  into  the 
chemical  substances  of  which  soil,  air,  and  water  are  com- 
posed. We  are  now  to  learn  by  experiments  the  charac- 
teristics of  some  of  these  materials  found  in  lifeless  things, 
and  some  of  the  combinations  of  these  materials  in  plants 
and  animals. 

I.   ELEMENTS,  COMPOUNDS,  AND  OXIDATION 

Materials:  Splinters  of  wood  and  pieces  of  carbon;  starch, 
sugar,  egg,  meat;  potassium  chlorate,  oxid  of  manganese, pieces  of 
marble,  zinc,  hydrochloric  acid,  lime  water  (see  below) ;  elements  for 
demonstration  (e.g.  phosphorus,  sulphur,  iron,  magnesium) ;  com- 
pounds for  demonstration  (e.g.  magnesium  sulphate,  sodium  nitrate, 
potassium  nitrate,  calcium  phosphate,  calcium  carbonate);  test 
tubes,  thistle  tube,  apparatus  stand,  tray  for  collecting  gases,  de- 
livery tube,  cylindrical  graduate  or  glass  jar.  (All  of  the  materials 
named  above  will  be  found  in  the  chemical  or  physical  laboratory 
of  almost  every  high  school.) 

Preparation  of  lime  water :  Put  into  a  large  bottle  a  good  handful 
of  lime  (freshly  slaked  in  water,  if  possible ;  air-slaked  lime  may  be 
used,  however).  Fill  the  bottle  with  water,  shake  the  mixture,  and 

5 


6  PLANT  BIOLOGY 

allow  it  to  stand  until  needed.  Then  pour  some  of  the  liquid  through 
a  funnel  in  which  is  a  filter  paper.  Collect  the  filtered  lime  water 
in  a  bottle,  and  keep  it  stoppered.  As  soon  as  it  becomes  cloudy, 
throw  it  away  and  obtain  some  more  clear  liquid  by  filtration  as  di- 
rected above.  The  large  bottle  can  be  kept  indefinitely  as  a  stock 
solution  if  it  is  kept  filled  with  water. 

9.  Carbon  (symbol,  C).  —  Laboratory  Study  No.  1.     Sug- 
gested as  home  work. 

1.  Prepare  some  charcoal  by  lighting  a  long  splinter  of  wood 

or  a  match  and  then  blowing  out  the  flame.  (Pre- 
pared charcoal  may  be  used.)  Charcoal  is  nearly 
pure  carbon. 

a.   Tell  what  you  have  done. 

6.  Is  carbon  (charcoal)  a  solid,  a  liquid,  or  a  gas  ?  What 
is  its  color  ? 

c.  Of  what  substance  does  this  experiment  prove  that 
wood  is  partly  composed  ? 

2.  Hold  the  tip  of  the  carbon  (charcoal)  in  a  hot  flame, 
a.   State  what  was  done. 

6.   Does  any  of  the  carbon  disappear  ? 

c.    Will  carbon  burn  ?     How  do  you  know  ? 

3.  State  three  characteristics  of  carbon  (charcoal)  that  you 

have  learned  from  these  experiments. 

4.  Hold  your  hand  over  the  glowing  charcoal  with  your  eyes 

closed.  How  can  you  still  tell  that  the  carbon  is 
burning  ? 

10.  Oxygen    (symbol,    O).  —  Laboratory    Study    No.    2. 
Demonstration . 

Preparation  of  oxygen:  Thoroughly  mix  a  teaspoonful  of  po- 
tassium chlorate  with  about  one-fourth  as  much  black  oxid  of  man- 
ganese. Put  the  mixture  in  a  large  test  tube.  Close  the  mouth  of 
the  test  tube  with  a  stopper  through  which  passes  a  delivery  tube, 
the  other  end  of  which  runs  beneath  the  surface  of  water  in  a  tray. 
Support  the  test  tube  in  a  slanting  position  on  an  apparatus  stand, 
and  heat  the  mixture  gently  with  a  gas  or  an  alcohol  flame,  until 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS      7 


the  oxygen  begins  to  be  given  off.  Fill  three  or  four  bottles  with 
water,  cover  each  with  a  piece  of  glass  or  cardboard,  and  invert  the 
first  one  over  the  mouth  of  the  delivery  tube,  removing  the  cover 
when  the  mouth  is  under  water.  Continue  to  heat  the  mixture 
until  the  bottle  is  full  of  oxygen,  then  cover  it  under  water  with  the 
glass  plate  or  cardboard,  and  stand  it  right  side  up  on  the  table. 
In  the  same  way  fill  as  many  jars  as  are  needed  for  the  experiments 
with  oxygen.  (Fig.  1.) 


FIG.  1.  —  Preparation  of  oxygen. 

Prepare  several  bottles  of  oxygen  as  directed  and  allow  them  to 
stand  until  all  fumes  have  settled,  before  answering  the  following 
questions. 

1.  Examine  a  bottle  of  oxygen. 
a.   State  what  you  have  done. 

6.   Do  you  find  oxygen  to  be  a  solid,  a  liquid,  or  a  gas  ? 
c.    State  whether  or  not  oxygen  has  color. 

2.  Heat  some  charcoal  (carbon)  till  it  glows  and  thrust  it 

into  a  bottle  of  oxygen. 

a.   Tell  what  was  done  and  describe  what  happens. 
6.   Does  carbon  burn  better  in  air  (which  is  a  mixture  of 

oxygen  and  other  gases)  or  in  pure  oxygen  ? 

3.  State  the  three  characteristics  of  oxygen  which  you  have 

learned. 

11.  Carbon  dioxid  (formula,  CO2).  —  Laboratory  Study 
No.  3.  Demonstration. 


8 


PLANT  BIOLOGY 


~7 


Preparation  of  carbon  dioxid:   Into   a  flask  put  some  pieces 
of  marble,  and  insert   a  stopper  through  which  passes  a  thistle 

tube  and  a  delivery  tube  like  that 
used  in  the  preparation  of  oxygen. 
Pour  into  the  thistle  tube  diluted 
hydrochloric  acid   until   the   lower 
end  of  this  tube  is  covered.     Col- 
lect a  bottle  of  carbon  dioxid  in 
the  same  way  that  oxygen  is  col- 
lected, keeping  the  mouth  of  the 
bottle  closed  with  a  glass  plate  or 
cardboard.      (Fig.   2.)      Prepare  a 
V  \\      /?*•    /      Bottle  of  carbon  dioxid  as  directed, 
\  N^T^    /       and  allow  it  to  stand  till  all  fumes 
of  carbon  nave  disappeared,  before  answering 
dioxid  or  of  hydrogen.  the  following  questions. 

1.  Examine  a  bottle  of  carbon  dioxid  and  state  whether  it 

is  a  solid,  a  liquid,  or  a  gas.  Compare  this  gas 
and  oxygen  as  to  color. 

2.  Light  a  splinter  of  wood  and  thrust  it  into  the  bottle  of 

carbon  dioxid. 

a.  Tell  what  was  done  and  describe  the  effect  of  the  carbon 

dioxid  upon  the  burning  splinter. 

b.  How  was  the  burning  splinter  or  carbon  affected  by 

oxygen? 

3.  Generate  some  carbon  dioxid  as  suggested  above  and  pass 

it  through  the  delivery  tube  into  a  test  tube  of 
clear  lime  water.  Tell  what  was  done  and  describe 
the  effect  of  carbon  dioxid  on  lime  water.  (Carbon 
dioxid  is  the  only  gas  that  affects  lime  water  in  this 
way;  hence  the  latter  is  a  reliable  test  for  carbon 
dioxid.) 

4.  State  the  four  characteristics  of  carbon  dioxid  which  you 

have  learned  from  these  experiments. 

5.  Place  in  a  bottle  of  pure  oxygen  a  piece  of  glowing 

carbon,  and  allow  it  to  burn  as  long  as  it  will. 
When  the  carbon  ceases  to  burn,  quickly  remove 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS      9 

it,  and  pour   in   some  clear  lime  water,  cork   the 

bottle,  and  shake. 
a.   Tell  what  was  done  and  describe  the  change  that  takes 

place  in  the  lime  water. 
6.    What   substance   is   evidently  formed  when   carbon 

burns  in  oxygen? 

6.  When  carbon  is   burned   in  oxygen,  the   two  unite   to 

form  a  new  substance  entirely  different  from 
either  carbon  or  oxygen.  This  new  substance  is 
called  carbon  dioxid,  because  it  is  composed  of  one 
part  of  carbon  and  two  of  oxgyen. 

a.  Describe  the  composition  of  carbon  dioxid. 

b.  State  the  method  by  which  carbon  dioxid  was  pro- 

duced in  this  experiment. 

7.  (Optional.)     By  means  of  a  glass  tube  blow  the  breath  from  the 

lungs  into  a  test  tube  of  lime  water, 
a.  What  change  do  you  notice  in  the  lime  water  ? 
6.  What  do  you  therefore  conclude  to  be  contained  in  the  breath 

from  the  lungs  ? 

12.  Hydrogen  (symbol,  H)  and  water  (formula,  H2O).  — 
Laboratory  Study  No.  4.  Demonstration. 

Preparation  of  hydrogen  (see  Caution  below) :  Into  a  flask  put 
some  pieces  of  zinc.  (See  Fig.  2.)  Insert  a  stopper  with  two  holes. 
Through  one  of  the  holes  pass  the  lower  end  of  a  thistle  tube  until 
it  nearly  touches  the  bottom  of  the  test  tube,  and  through  the  other 
run  a  short  piece  of  glass  tubing.  To  the  upper  end  of  the  latter 
attach  by  means  of  a  piece  of  rubber  tubing  a  delivery  tube  that  will 
reach  beneath  the  surface  of  a  tray  of  water  such  as  that  used  in 
collecting  oxygen  and  in  the  preparation  of  carbon  dioxid.  Pour 
through  the  thistle  tube  enough  diluted  hydrochloric  acid  to  cover 
the  lower  end  of  the  thistle  tube.  (If  hydrogen  does  not  come  off 
rapidly  enough,  put  into  the  flask  a  bit  of  copper  sulphate.)  After 
the  hydrogen  has  been  given  off  for  several  minutes,  collect  a  bottle 
over  water  in  the  same  manner  as  in  the  oxygen  experiment.  Re- 
move the  bottle,  holding  it  upside  down,  and  place  it  on  the  desk 
in  this  position.  Allow  the  bottle  to  stand  till  fumes  disappear. 


10  PLANT  BIOLOGY 

Caution :  If  in  3  below  an  explosion  occurs,  collect  another  bottle 
of  hydrogen  before  answering  the  questions,  for  an  explosion  indi- 
cates that  oxygen  is  mixed  with  the  hydrogen,  and  such  a  mixture 
is  dangerous  to  experiment  with. 

1 .  Examine  a  bottle  of  hydrogen,  and  state  whether  hydrogen 

is  a  solid,  a  liquid,  or  a  gas.  Compare  its  color  with 
that  of  oxygen  and  carbon  dioxid. 

2.  Thrust  a  lighted  stick  up  into  the  mouth  of  an  inverted 

bottle  of  hydrogen.  (This  experiment  will  be  more 
satisfactory  if  the  room  is  darkened.) 

a.  State  what  was  done  and  tell  how  the  hydrogen  af- 

fected the  burning  stick. 

b.  How  does  the  burning  stick  affect  the  hydrogen? 

c.  What  is  one  difference  between  oxygen  and  hydrogen  ? 

d.  What  is  one  difference  between  hydrogen  and  carbon 

dioxid  ? 

3.  If  hydrogen  is  not  being  given  off  from  the  delivery  tube 

in  sufficient  quantity,  pour  into  the  thistle  tube 
some  hydrochloric  acid.  Detach  the  delivery  tube 
from  the  rubber  tube  of  the  hydrogen  apparatus 
and  insert  in  its  place  a  piece  of  glass  tubing,  the 
upper  end  of  which  is  drawn  out  to  a  small  diameter. 
Collect  some  of  the  gas  in  a  test  tube  by  displacement 
of  air  and  light  it.  When  it  burns  with  only  a  slight 
puff,  apply  a  lighted  match  to  the  hydrogen  escap- 
ing from  the  drawn-out  tube. 

Hold  over  the  flame  a  bottle  which  is  clean  and  dry. 

a.   Describe  the  preparation  of  this  experiment. 

6.    What  do  you  find  on  the  inside  of  the  glass? 

c.    What,  therefore,  is  formed  when  hydrogen  burns  ? 

4.  When  hydrogen  burns,  it  unites  with  the  oxygen  of  the 

air  and  forms  oxid  of  hydrogen,  more  commonly 
known  as  water  (formula,  H20). 

a.  In  what  respect  does  hydrogen  differ  from  oxid  of 

hydrogen  (water)  in  its  most  common  form  ? 

b.  State  how  oxid  of  hydrogen  was  formed. 

c.  In  what  respects  is  the  method  of  producing  oxid  of 

hydrogen  (water)  the  same  as  that  of  producing 
oxide  of  carbon  (carbon  dioxid)  ?  (See  11,5  above.) 

5.  Name  five  characteristics  of  hydrogen. 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS     11 

13.  Nitrogen  (symbol,  N)  and  the  composition  of  the  air. 
—  Laboratory  Study  No.  5:  Demonstration. 

Fasten  a  candle  to  a  piece  of  cardboard  and  float  the  latter  on  a 
tray  of  lime  water.  Light  the  candle,  and  cover  the  flame  with 
an  inverted  wide-mouthed  bottle,  bringing  the  latter  slowly  down 
until  the  edge  rests  on  the  bottom  of  the  tray.  Allow  the  candle 
to  burn  as  long  as  it  will.  Then  turn  the  bottle  right  side  up,  cover- 
ing the  mouth  with  the  cardboard,  keeping  inside  the  bottle  the  lime 
water  that  has  risen  to  take  the  place  of  the  oxygen.  Shake  the 
contents  of  the  bottle,  to  make  the  lime  water  absorb  the  carbon 
dioxid,  and  allow  it  to  stand  till  the  upper  part  of  the  jar  is  clear. 
Keep  the  bottle  covered  to  prevent  the  mixing  of  air  with  the 
nitrogen. 

1.  Examine  a  bottle  of  nitrogen.     Is  it  a  solid,  a  liquid,  or  a 

gas  ?     What  is  its  color  ? 

2.  Thrust  a  burning  splinter  of  wood  into  the  nitrogen. 

a.  Tell  what  was  done.     Does  the  wood   continue  to 

burn? 

b.  Does  the  nitrogen  burn? 

c.  In  what  respect  does  nitrogen  differ  from  oxygen? 

3.  State  four  characteristics  of  nitrogen. 

4.  Why  does  carbon  burn  faster  in  oxygen  than  in  air? 

5.  Air  consists  principally  of  oxygen  and  nitrogen.     The 

water  in  the  bottle  represents  the  amount  of  oxygen 
there  was  in  the  bottle  of  air,  and  the  nitrogen 
occupies  the  rest  of  the  space. 

a.  About  what  fractional  part  of  the  air  in  the  bottle  was 
oxygen  ? 

6.  What  fractional  part  of  the  air  in  the  bottle  is  nitro- 
gen ? 

6.  Expose  to  the  air  of  the  room  for  a  half  hour  or  more  a 

dish  with  some  clear  lime  water, 
a.   Describe  the  experiment,  stating  the  effect  on  the  lime 

water. 
6.    What  substance  does  this  experiment  prove  to  be 

present  in  air? 


12  PLANT  BIOLOGY 

II.   DEFINITIONS 

14.  A  chemical  element  is  a  ..substance  that  has   never 
been  separated  into  two  or  more  different  kinds  of  matter.1  — 
Over  seventy  of  these  elements  are  known  at  the  present  time, 
and  of  these  seventy,  twelve  are  found  constantly  in  the  liv- 
ing substance  of  plants  and  animals.     The  most  common  of 
these  twelve  elements  are  carbon    (symbol,  C),   hydrogen 
(H),  oxygen  (0),  nitrogen  (N),  sulphur  (S),  phosphorus  (P), 
iron  (Fe),  and  calcium  (Ca),  which  is  found  in  lime. 

[In  addition  to  the  elements  already  studied  (C,  0,  H,  N), 
the  others  mentioned  should  be  shown  to  students;  and  if 
time  permits,  some  of  these  elements  may  be  burned  or  oxi- 
dized in  oxygen  and  the  characteristics  of  the  oxids  thereby 
formed  may  be  discussed.] 

15.  A  chemical  compound  is  a  substance  formed  by  the 
union  of  two  or  more  chemical  elements.  —  Two  of  the  im- 
portant compounds  considered  in  biology  are  carbon  dioxid 
(formula  CO2) ,  which  means  that  it  is  composed  of  one  part 
of  carbon  and  two  parts  of  oxygen,  and  water  (formula  H2O), 
which  means  that  it  is  composed  of  two  parts  of  hydrogen  and 
one  part  of  oxygen. 

16.  A  mixture  differs  from  a  compound  in  the  fact  that 
the  elements  or  compounds  of  which  the  former  is  composed 
are  not  chemically  united.  —  In  air,  for  instance,  the  oxygen 
and  nitrogen  are  not  chemically  combined,  but  are  simply 
put  together  as  one  might  mix  pepper  and  salt.     Again,  when 
sugar  is  dissolved  or  mixed  with  water,  the  two  compounds 
are  mingled  so  closely  that  the  sugar  disappears;    it  may 
easily  be  obtained  unchanged  in  its  composition  by  evaporat- 
ing the  water. 

1  There  are,  however,  exceptions  to  this  statement,  but  they  are 
too  technical  for  discussion  in  an  elementary  text-book. 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS     13 

17.  Oxidation  is  the  chemical  union  of  oxygen  with  some 
other  substance.  —  It  may  take  place  slowly,  as  when  carbon 
is  made  to  glow  in  the  air ;   or  it  may  take  place  rapidly,  as 
when  carbon  burns  in  oxygen.     But  whenever  oxidation  takes 
place,  (1)  an  oxid  is  formed,  (2)  a  certain  amount  of  heat  is 
produced,  and  (3)  if  the  process  is  sufficiently  rapid,  a  flame 
is  seen. 

III.     A  STUDY  OF  THE  FOOD  SUBSTANCES 

18.  Introduction.  —  The  food  substances  needed  by  plants 
and   animals   may   be   divided   into   five   classes,   namely : 
(1)  carbohydrates  (i.e.  starches  and  sugars) ;   (2)  fats  and  oils; 
(3)  proteins,1  which  are  also  known  as  albuminous  or  nitrog- 
enous substances    (e.g.,  white  of  egg,  lean  meat,  gluten  of 
wheat) ;  (4)  minerals  (e.g.  common  salt,  saltpeter,  phosphate 
of  lime) ;   (5)  water. 

19.  To  determine  the  chemical  composition  of  starch.  — 

Laboratory  Study  No.  6.     Suggested  as  home  work. 

Warm  some  starch  in  an  old  cooking  spoon  in  order  to 
drive  off  any  water  that  may  be  in  it,  but  do  not  allow  it 
to  burn.  To  determine  when  the  starch  is  free  from  water, 
hold  the  heated  starch  under  a  dry,  cold  tumbler,  and  if  no 
moisture  collects  upon  the  tumbler,  the  starch  contains  no 
water.  Now  set  the  starch  on  fire,  and  hold  a  cold,  dry 
glass  over  the  burning  starch. 

1.  Tell  what  you  have  done  and  state  what  is  formed  on  the 

inside  of  the  tumbler  by  the  burning  of  the  starch. 

2.  What  is  the  only  chemical  element  that  could  possibly 

form  water  by  burning  (i.e.  by  uniting  with  oxygen)  ? 

3.  What  chemical  element,  therefore,  must  have  been  pres- 

ent in  the  starch  in  order  to  have  produced  water  when 
dry  starch  is  burned? 

1  The  term  protein  is  used  throughout  this  book  instead  of  proteid, 
because  of  the  unanimous  recommendation  in  favor  of  the  former 
term  by  the  American  Society  of  Biological  Chemists  and  the 
American  Physiological  Society.  See  Science,  April  3,  1908. 


14  PLANT  BIOLOGY 

4.  What  substance  is  left  in  the  cooking  spoon  after  the 

flame  goes  out? 

5.  Name  two  chemical  elements  present  in  starch. 

6.  Starch  also  contains  oxygen.     Name  now  the  three  chem- 

ical elements  of  which  this  nutrient  is  composed. 

20.  To    determine    the    chemical    composition    of    sugar, 
fat,  and  protein.  —  Laboratory  Study  No.  7.     (Optional.) 

1.  Test  sugar  in  the  same  way  as   directed  in  Laboratory  Study 

No.  6,  1-5  (above). 

a.  Describe  each  of  the  experiments,  giving  results   and   con- 

clusions. 

b.  Sugar,  like  starch,  has  oxygen  also  in  its  composition.     Name 

now  all   the  chemical  elements  of  which  sugar  is  com- 
posed. 

2.  In  a  similar  way  test  a  fat  (e.g.  lard,  or  the  fat  of  meat). 

a.  State  what  you  do,  what  you  see,  and  what  you  conclude. 
b:  Fat,  like  starch  and  sugar,  has  oxygen  in  its  composition,  but 

in   a    different   proportion.      State,    therefore,  the    three 

elements  present  in  fat. 

3.  (Demonstration.)      Secure    a  vegetable    protein    (e.g.  gluten) 

and  test  it  as  directed  above. 

a.  Describe  your  experiments  and  give  your  results  and  con- 
clusions. 

6.  Besides  the  two  elements  you  have  shown  to  be  present, 
protein  also  contains  oxygen,  nitrogen,  sulphur,  phos- 
phorus, and  often  other  elements.  State,  now,  the 
chemical  elements  of  which  this  food  substance  is  com- 
posed. 

21.  Summary.  —  The  carbohydrates,  as  we  have  learned 
and  as  their  name  implies,  are  composed  of  the  chemical  ele- 
ments carbon,  hydrogen,  and  oxygen.     The  same  three  chemi- 
cal elements  are  likewise  present  in  fats  and  proteins,  but  in 
different  proportions.     Proteins,  however,  in  addition  to  the 
carbon,  hydrogen,  and  oxygen,  contain  at  least  three  other 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS     15 

chemical  elements,  namely,  nitrogen,  sulphur,  and  phos- 
phorus; in  fact,  proteins  are  the  most  complex  of  all  chemical 
substances  known. 

Following  is  the  composition  of  the  various  nutrients  stud- 
ied thus  far :  — 

Starch,  composed  of  C,  H,  0  (in  the  proportion  of  C6Hi005). 

Sugar,  composed  of  C,  H,  O.    (Grape  sugar  =  C6H1206.) 

Fat,  composed  of  C,  H,  O. 

Protein,  composed  of  C,  H,  0,  N,  S,  P  (and  sometimes  of 
other  elements). 

22.  Tests    for    the    food    substances.  —  Having    demon- 
strated that  the  various  food  substances  are  chemical  com- 
pounds, each  composed  of  several  chemical  elements,  we  are 
now  to  carry  on  experiments  by  which  it  will  be  possible  to 
test  for  each  of  these  food  substances.     By  this  means  we 
shall  be  able  to  prove  the  presence  or  absence  of  starch,  grape 
sugar,  protein,  fat,  mineral  matters,  and  water  in  the  foods 
used  by  plants,  animals,  and  man. 

23.  To  test  foods  for  starch.     Laboratory  Study  No.  8. 

Materials:  Corn  starch,  grape  sugar,  white  of  egg,  fat  or  oil, 
salt,  water;  various  foods  in  the  home  kitchen;  iodine  solution 
(see  below) ;  test  tubes;  gas  burner  or  alcohol  lamp. 

Preparation  of  iodine  solution:  A  quart  (1000  cc.)  of  iodine  solu- 
tion is  made  by  dissolving  in  5  teaspoonfuls  (40  cc.)  of  water,  one- 
half  teaspoonful  (4  grams)  of  potassium  iodide,  and  one-fourth 
this  amount  of  iodine  (1  gram).  This  solution,  when  thoroughly 
mixed,  should  be  diluted  to  make  one  quart  (1000  cc.).  In  a  clean 
bottle  this  mixture  will  keep  indefinitely.1 

1.  Put  a  small  amount  (size  of  a  pinhead)  of  corn  starch 
in  a  test  tube,  add  water,  shake  the  mixture,  and  boil 
it  over  a  gas  flame.  Pour  into  the  starch  mixture 

1  From  Peabody's  "  Laboratory  Exercises."    Henry  Holt  &  Co. 


16  PLANT  BIOLOGY 

thus  formed  a  few  drops  of  iodine.  What  color  is 
produced  ? 

2.  Try  the  effect  of  iodine  on  each  of  the  other  food  sub- 

stances as  follows :  Put  a  small  amount  of  grape  sugar 
into  a  test  tube;  into  a  second  tube  put  some  white 
of  egg  (protein) ;  into  a  third  some  fat  or  oil ;  into  a 
fourth  some  mineral  matter  (salt) ;  and  into  a  fifth  some 
water.  Add  a  little  water  to  each  and  boil  as  in  1 
above  to  cook  each  nutrient.  Add  a  drop  or  two  of 
iodine  solution  to  each  test  tube. 

Do  any  of  the  colors  thus  produced  resemble  at  all  the 
color  resulting  from  the  addition  of  iodine  to  starch  ? 

3.  From  the  preceding,  state  how  you  can  determine  whether 

or  not  a  substance  contains  starch. 

4.  (Optional  home  work.)     Test  as  many  foods  as  you  can  (e.g. 

oatmeal,  flour,  raw  meat,  milk,  parsnip,  potato,  onions,  ap- 
ples, beans,  rice,  pepper)  in  the  following  way :  Put  a  small 
amount  of  a  given  food  into  a  test  tube  or  in  a  sauce  pan,  add 
a  little  water,  and  boil  to  cook  each  food,  then  add  a  few 
drops  of  iodine.  Before  making  each  test  make  sure  that  the 
test  tube  or  saucer  is  clean.  Prepare  in  your  note-book  a 
table  like  the  following,  and  fill  in  under  each  head  the  names 
«  of  the  foods  you  have  proved  to  contain  or  to  be  without 
starch. 


STARCH  PRESENT 

STARCH  ABSENT 

24.  To  test  foods  for  grape  sugar.  Laboratory  Study 
No.  9. 

Materials :  Grape  sugar,  corn  starch,  white  of  egg,  fat  or  oil,  salt, 
water ;  various  food  substances  common  in  home  kitchen ;  Fehling's 
solution  (see  below) ;  test  tubes,  gas  burner  or  alcohol  lamp. 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS      17 

Preparation  of  Fehling's  Solution:  —  To  make  Fehling's  solution 
dissolve  3  teaspoonfuls  (34.64  grams)  of  pure  pulverized  copper  sul- 
phate (blue  vitriol)  in  a  little  less  than  a  half-pint  of  water  (200  cc.). 
Make  a  second  solution  by  dissolving  in  a  pint  (500  cc.)  of  water 
twelve  heaping  teaspoonfuls  (150  grams)  of  Rochelle  salt  and  3  (5- 
inch)  sticks  of  caustic  soda  (50  grams).  Fehling's  solution  does  not 
keep  for  any  great  length  of  time,  and  hence  must  be  made  up  fresh 
a  short  time  before  it  is  needed.  To  do  this,  thoroughly  mix  two 
volumes  of  the  copper  sulphate  solution  and  five  volumes  of  the 
solution  of  Rochelle  salt  and  caustic  soda,  and  dilute  the  mixture 
with  an  equal  volume  of  water.  It  is  more  convenient  to  prepare 
it  in  small  quantities  from  the  tablets  that  may  be  obtained  of 
druggists.  Before  making  any  tests  boil  a  small  quantity  of  the 
Fehling's  solution  in  a  clean  test  tube.  If  it  retains  its  transparent 
blue  color,  it  is  ready  for  use;  otherwise  a  fresh  supply  must  be 
prepared.1 

1.  Dissolve   a  small  amount    of  grape  sugar    (glucose)  in 

water  in  a  test  tube.  Add  some  Fehling's  solution  and 
boil.  What  change  in  color  do  you  notice? 

2.  Try  the  effect  of  Fehling's  solution  on  each  of  the  other 

food  substances  as  follows:  Put  a  small  amount  of  starch 
into  a  test  tube;  into  a  second  tube  some  white  of  egg; 
into  a  third  tube  some  fat  or  oil;  into  a  fourth  tube  some 
mineral  matter  (salt) ;  and  into  a  fifth  tube  some  water. 
Add  a  little  water  to  each  tube,  then  pour  in  a  small 
amount  of  Fehling's  solution  and  boil  as  in  1  above.  Do 
any  of  the  colors  produced  resemble  at  all  the  color  of 
the  Fehling's  solution  when  it  was  boiled  with  grape  sugar? 

3.  From  the  preceding  experiments  state  how  you  can  deter- 

mine whether  or  not  a  substance  contains  grape  sugar. 

4.  (Optional.)     Test  as   many   foods    as  you    can    (e.g.  onions, 
grapes,  pears,  granulated  sugar,  honey,  molasses,  parsnip,  raw 
meat,  milk,  egg)  in  the  following  manner :  Put  a  small  amount 
of  a  given  food  into  a  test  tube,  add  a  little  water,  and  a 

^rom  Peabody's  "Laboratory  Exercises."    Henry  Holt  &  Co., 
New  York, 
c 


18  PLANT  BIOLOGY 

small  spoonful  of  Fehling's  solution,  and  boil.  Before  making 
each  test  make  sure  that  the  test  tube  is  clean.  Prepare  in 
your  note-book  a  table  like  the  following,  and  fill  in  under 
each  head  the  names  of  the  foods  you  have  proved  to  contain 
or  to  be  without  grape  sugar. 


GRAPE  SUGAR  PRESENT 

GRAPE  SUGAR  ABSENT 

25.  To  test  foods  for  proteins  (albuminous  or  nitrogenous 
substances).  —  Laboratory  Study  No.  10. 

Materials :  White  of  egg,  corn  starch,  grape  sugar,  mutton  tallow 
or  other  fat,  salt,  water ;  piece  of  meat,  milk ;  concentrated  nitric 
acid,  ammonia ;  test  tubes;  gas  or  alcohol  lamp. 

1.  Pour  a  little  concentrated  nitric  acid  on  a  piece  of  hard 

boiled  egg  in  a  test  tube. 

a.  What  change  in  color  of  the  egg  do  you  observe  ? 

b.  (Optional.)     Wash  the  egg  with  water,  add  a  little  concen- 

trated ammonia,  and  note  result. 

2.  Try  the  effect  of  nitric  acid  on  each  of  the  other  food  sub- 

stances as  follows:  Put  a  small  amount  of  starch 
into  a  test  tube;  into  a  second  tube  some  grape 
sugar;  into  a  third  some  mutton  tallow  or  other 
fat ;  into  a  fourth  some  mineral  matter  (salt) ; 
and  into  a  fifth  tube  some  water.  Add  a  little  con- 
centrated nitric  acid  to  each  of  these  foods.  Is 
any  color  produced  like  that  resulting  from  adding 
nitric  acid  to  protein?  (In  case  a  liquid  is  to  be 
tested  with  nitric  acid,  the  mixture  should  be  boiled 
before  deciding  whether  protein  is  present  or  absent.) 

3.  From  the  preceding  experiments  state  how  you  can  deter- 

mine whether  or  not  a  food  contains  protein. 


COMPOSITION   OF  LIFELESS  AND  LIVING   THINGS      19 

4.  (Optional.)  Prepare  in  your  note-book  a  table  like  the  follow- 
ing, and  place  in  the  proper  columns  the  names  of  the 
foods  tested  in  class. 


PROTEIN  PRESENT 

PROTEIN  ABSENT 

26.  To  test  foods  for  fats.  —  Laboratory  Study  No.  11. 
Suggested  as  home  work. 

Materials :  Butter  or  olive  oil,  corn  starch,  grape  sugar,  piece  of 
boiled  white  of  egg,  salt,  water ;  various  foods  in  the  home  kitchen, 
including  nuts. 

1.  Put  on  a  piece  of  paper  a  piece  of  butter  half  the  size  of 

a  pea  (or  a  drop  of  olive  oil).  Put  the  paper  in  a 
warm  place  (e.g.  in  a  hot  oven  or  over  a  heated  radi- 
ator) for  a  few  moments,  then  hold  the  paper  between 
yourself  and  the  light.  How  is  the  paper  affected  by 
the  fat? 

2.  Try  the  effect  of  each  of  the  other  food  substances  (starch, 

grape  sugar,  piece  of  boiled  egg,  i.e.  protein,  salt,  i.e. 
mineral  matter,  water)  on  paper,  by  adding  an  equal 
quantity  (half  the  size  of  a  pea)  of  each  to  separate 
pieces  of  paper.  Put  the  pieces  of  paper  in  a  warm 
place  as  in  1  above.  Hold  each  piece  between  yourself 
and  the  light.  Do  any  of  these  food  substances  affect 
the  paper  as  did  the  fat  ? 

3.  From  the  preceding  experiments  state  how  you  can  de- 

termine whether  or  not  a  food  contains  fat. 

4.  (Optional.)     Prepare  in  your  note-book  a  table  like  the  follow- 

ing, and  place  in  the  proper  columns  the  names  of  the  foods 
tested  at  home  or  in  class. 


20  PLANT  BIOLOGY 


FAT  PRESENT 

FAT  ABSENT 

NOTE.  In  case  a  food  which  is  being  tested  may  possibly  contain 
a  small  amount  of  fat,  the  food  should  be  pulverized,  shaken  in  a 
test  tube  with  ether  or  benzine  (to  dissolve  out  the  fat) ,  and  allowed 
to  stand  for  24  hours.  The  clear  liquid  should  then  be  poured  upon 
paper,  and  the  ether  or  benzine  allowed  to  evaporate. 

Caution.  Never  handle  ether  or  benzine  near  a  flame  or  hot  stove, 
since  the  vapor  of  these  substances  is  very  inflammable. 

27.  To  test  foods  for  mineral  matter.     Laboratory  Study 
No.  12.     Demonstration. 

Materials:  Salt,  corn  starch,  grape  sugar,  piece  of  boiled  egg, 
butter  or  fat,  water. 

1.  Place  a  piece  of  salt  half  the  size  of  a  pea  on  an  old  cook- 

ing spoon  and  heat  over  as  hot  a  flame  as  possible. 
Does  the  salt  burn  and  disappear? 

2.  In  the  same  manner  try  the  effect  of  heat  on  the  other 

food  substances  (starch,  grape  sugar,  white  of  egg,  fat, 
water).    Do  any  of  these  substances  burn  or  disappear? 

3.  From  the  preceding  experiments  state  how  you  can  deter- 

mine whether  or  not  a  food  contains  mineral  matter. 

4.  (Optional  home  work.)     Test  at  home  in  the  same  manner  as 

described  in  1  above  a  match  stick  and  a  leaf.     Do  these 
plant  materials  contain  mineral  matters  ?    How  do  you  know  ? 

28.  To  test  foods  for  water.  —  Laboratory  Study  No.  13. 
Home  work. 

1.  Warm  a  little  water  on  a  spoon  and  place  over  it  a  dry, 
cool,  tumbler.  What  do  you  see  on  the  inside  of  the 
glass?  How,  then,  can  you  tell  whether  or  not  water 
is  found  in  a  given  food  ? 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS      21 


2.  (Optional.)     Test  as  many  foods  as  you  can  by  warming  in  turn 

a  small  quantity  of  each  in  a  spoon  (without  letting  the  food 
burn),  and  holding  over  the  spoon  a  dry,  cool  tumbler. 
What  do  you  learn  as  to  the  presence  of  water  in  foods  ? 

3.  (Optional  Demonstration.)     To  determine  the  amount  of  water 

in  potatoes: 

a.  Remove  a  thin  layer  of  peel  from  a  potato,  weigh  the  potato, 
and  lay  it  aside  in  a  warm  dry  place  (protected  from  mice). 
Weigh  each  day,  and  fill  out  in  your  note-book  for  each 
day  the  first,  third,  and  fifth  columns  in  a  table  like  the 
following : 


WEIGHT  OF  POTATO 

Loss  OF  ORIGINAL  WT. 

PER  CENT  OF  Loss 

Without 
Peel 

With 
Peel 

Without 
Peel 

With 
Peel 

Without 
Peel 

With 

Peel 

j 

First  day 
Second  day 
Third  day 
Fourth  day 
etc. 













b.  Secure  a  second  potato  about  the  same  size  as  the  first,  weigh 

it  each  day,  and  place  it  beside  the  potato  that  was  peeled. 
Record  results  and  percentages  for  each  day  in  second, 
fourth,  and  sixth  columns  of  preceding  table. 

c.  Which  of  the  two  potatoes  decreases  in  weight  the  more 

rapidly  ?  Almost  all  the  loss  of  weight  is  due  to  the  evapo- 
ration of  water;  what  do  you  infer,  therefore,  as  to  one 
use  of  the  peel  ? 

d.  Continue  to  weigh  the  potato  without  the  peel  at  intervals 

until  there  is  no  further  loss.  What  percentage  of  potato 
is  water?  When  potatoes  are  bought  at  $3  per  barrel, 
how  much  of  this  sum  is  paid  for  water  ? 


22  PLANT  BIOLOGY 


IV.     MANUFACTURE  OF  THE  FOOD  SUBSTANCES  BY  PLANTS 

29.  Is  starch  present  in  the  green  leaves  of  a  plant  that 
has  been  exposed  to  sunlight?  —  Laboratory  Study  No.  14. 

Take  several  leaves  from  a  vigorous  plant  (e.g.  geranium, 
hydrangea)  which  has  been  exposed  to  bright  sunlight  for 
a  number  of  hours.  Boil  them  a  few  moments  in  a  large  test 
tube  or  flask  of  water ;  pour  off  the  water,  add  alcohol,  and 
boil  carefully  over  a  piece  of  wire  gauze  or  asbestos  until  all 
the  green  coloring  matter  has  been  removed.  Rinse  the  leaves 
in  water,  add  iodine  solution,  and  spread  the  leaves  on  saucers, 
or  in  Petri  dishes. 

1.  Describe  in  your  own  words  how  the  experiment  was 

performed. 

2.  Is  starch  present  in  the  leaves  ?     How  do  you  know  ? 

3.  Why  was   it   necessary   to   remove  the  green   coloring 

matter  from  the  leaves  before  testing  for  starch?     (If 
you  are  in  doubt,  add  some  iodine  to  green  leaves.) 

4.  (Optional.)     How  may  grass  stains  be  removed  from  clothing  ? 

30.  Is  starch  present  in  the  green  leaves  of  a  plant  that 
has  been  deprived  of  sunlight?1  —  Laboratory  Study  No.  15. 

Put  a  vigorous  plant  (e.g.  fuchsia,  squash,  sunflower,  or 
bean  seedling)  in  darkness  for  48  hours  or  more.  Remove 
several  leaves,  and  treat  them  as  described  in  29  above. 

1.  State  briefly  how  the  preparation  of  this  experiment  dif- 

fers from  that  in  the  previous  experiment. 

2.  Give  your  observation  and  conclusion. 

3.  State,  therefore,  whether  sunlight  is  or  is  not  necessary 

for  the  manufacture  of  starch  in  green  leaves. 

31.  Is  starch  present  in  colorless  portions  of  green  leaves? 

—  Laboratory  Study  No.  16. 

1  A  most  suggestive  series  of  experiments  on  the  formation  of 
starch  in  green  leaves  is  found  in  the  Botanical  Gazette  for  September, 
1909,  pp.  224-228,  by  Sophia  Eckerson,  of  Smith  College. 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS     23 


Secure  a  plant  having  some  portions  that  are  colorless  (e.g. 
striped  grass).  Expose  the  plant  to  sunlight  for  two  or  three 
hours,  then  remove  several  leaves  and  test  them  in  the  same 
manner  as  described  in  29  above. 

1.  State  briefly  how  the  preparation  of  this  experiment 

differs  from  that  of  the  two  preceding  experiments. 

2.  What  is  your  observation  and  conclusion  as  to  the  pres- 

ence of  the  starch  in  the  green  and  colorless  portions  ? 

3.  State,  therefore,  whether  green  material  is  or  is  not  neces- 

sary for  the  manufacture  of  starch. 

This  green  material  in  leaves  is  called  chlorophyll  (from 
Greek  chloros  =  green  +  phullon  =  leaf). 

32.  Is  carbon  dioxid  necessary  for  starch  manufacture  in 
leaves?  —  Laboratory  Study  No.  17. 

Secure  two  vigorous  potted  plants,  two  bell-jars  large 
enough  to  go  over  the  plant  and  pot,  and  two  trays  or  other 
receptacles  having  a  greater  di- 
ameter than  that  of  the  bell-jar. 
Place  the  plants  in  darkness  for  24 
hours  at  least,  so  that  the  leaves 
may  be  free  from  starch  (see  30 
above).  Now  test  the  leaves  of 
both  plants  to  make  sure  they 
are  free  from  starch.  Into  one 
tray  pour  a  quantity  of  lime  water 
and  into  the  other  tap  water. 
Put  the  plants  on  supports  of 
some  kind  so  that  the  pots  will 
not  touch  the  liquid,  and  cover 
with  the  bell-jars.  (See  Fig.  3.) 
Be  sure  that  the  edges  of  the  bell- 
jars  are  covered  with  the  liquid, 
so  that  no  air  can  enter  the  jars.  Place  both  preparations 
where  the  plants  can  get  no  sunlight  for  24  hours  in  order 
to  give  time  for  the  absorption  of  carbon  dioxid  in  the  jar 
with  the  lime  water.  Place  both  preparations  in  strong 
sunlight  for  several  hours. 


FIG.  3.  —  Apparatus  for  demon- 
strating the  relation  of  carbon 
dioxid  to  starch  manufacture. 


24  PLANT  BIOLOGY 

/ 

1.  Describe  the  preparation  of  the  experiment. 

2.  Examine  the  lime  water  inside  the  bell-jar.     What  proof 

have  you  that  carbon  dioxid  has  been  absorbed  ? 

3.  Remove  a  leaf  from  each  of  the  plants  and  test  for  starch. 

Tell   what   was   done    and    state   your   observations. 
Which  leaf,  therefore,  contains  starch? 

4.  What  is  your  conclusion  as  to  the  necessity  of  carbon 

dioxid  for  starch  manufacture? 

5.  What  chemical  elements  that  are  present  in  starch  might 

be  furnished  by  the  carbon  dioxid  (CO2)  ? 

6.  The  other  raw  material  needed  by  plants  for  the  manu- 

facture of  starch  is  water  (H2O) .     What  third  chemical 
element  found  in  starch  must  be  furnished  by  water? 

7.  Now  name  the  two  raw  materials  used  by  plants  in  the 

manufacture  of  starch  and  state  the  chemical  elements 
which  each  can  furnish. 

33.  Manufacture  of  carbohydrates.  —  The  substance  first 
made  by  the  combination  of  carbon,  hydrogen,  and  oxygen 
in  the  leaves  is  not  starch,  but  a  simple  carbohydrate  which 
is  then  made  into  grape  sugar.     When  the  plant  manufactures 
more  sugar  than  it  needs  for  immediate  use,  the  surplus  is 
changed  to  starch,  and  this  is  what  we  have  found  stored  in 
the  leaves. 

34.  Manufacture  of  proteins.  —  We  have  already  learned 
that  proteins  contain  carbon,  hydrogen,  oxygen,  nitrogen, 
and  usually  sulphur  and  phosphorus  (see  21).     The  plant, 
therefore,  must  somehow  obtain  these  elements  in  order  to 
manufacture    proteins.     It    has    been   proved    that    plants 
manufacture  sugar,  and  this  probably  supplies  the  necessary 
carbon,  hydrogen,  and  oxygen.     The  nitrogen  that  is  needed 
is  furnished  by  compounds  containing  nitrogen  such  as  salt- 
peter (potassium  nitrate,  KNO3),  and  the  sulphur  and  phos- 
phorus are  secured  from  mineral  compounds  known  as  sul- 
phates and  phosphates.     These  compounds  are  derived  from 
soil  water.     From  these  compounds,  namely,  sugar  and  the 


COMPOSITION   OF  LIFELESS  AND  LIVING    THINGS      25 

mineral  matters  containing  nitrogen,  sulphur,  and  phos- 
phorus obtained  from  the  soil,  the  living  plant  manufactures 
protein. 

35.  Do  green  plants  give  off  a  gas  in  sunlight?  —  Labora- 
tory Study  No.  18. 

Into  a  glass  cylinder  containing  water  fresh  from  the  faucet 
put  a  small  amount  of  water  plant  (Elodea,  Spirogyra,  or 
Milfoil),  holding  it  to  the  bottom  of  the  tall  jar  by  means  of 
a  weight  if  necessary.  Stand  the  cylinder  in  direct  sunlight. 

1.  Describe  the  preparation  of  the  experiment. 

2.  What  do  you  observe  coming  off  from  the  plant  ?     (These 

bubbles  of  gas  have  been  proved  to  be  composed  of 
oxygen.) 

36.  Do  green  plants  give  off  a  gas  when  deprived  of  sun- 
light? —  Laboratory  Study  No.  19. 

Place  the  glass  cylinder  prepared  as  directed  above  in 
darkness  for  several  hours  (or,  still  better,  a  second  cylinder 
should  be  used  for  comparison). 

1.  In  what  respects  do  Experiments  18  and  19  differ? 

2.  Do  you  see  any  bubbles  as  long  as  the  cylinder  is  kept 

in  the  dark? 

3.  Under  what  condition,  therefore,  does  a  green  plant  give 

off  oxygen? 

37.  The  oxygen  supply  for  animals.  —  We  have  seen  that 
starch  is  made  of  carbon  dioxid  (C02)  and  water  (H20).     By 
repeated  experiments  biologists  have  proved  that  in  the  pro- 
cess of  manufacturing  carbohydrates  more  oxygen  is  present 
in  the  CO2  and  H^O  than  is  needed.     This  is  the  oxygen  we 
have  seen  given  off  by  the  green  water  plant  in  sunlight. 
Every  green  plant  gives  off  oxygen  into  the  air  when  manu- 
facturing carbohydrates.     Hence,  in  this  process  the  carbon 
dioxid  is  constantly  being  taken  from  the  air  and  a  fresh 
supply  of  oxygen  set  free. 


CHAPTER  III 


THE   STRUCTURE   OF   PLANTS 


38.    The  parts  of  a  plant.  —  Laboratory  Study  No.  20. 

Materials:  A  well-developed  bean  plant  or  other  seedling  or  a 
weed,  for  each  two  pupils ;  one  or  more  plants  with  flowers  and  if 
possible  with  fruits  for  demonstration. 

Nearly  all  the  plants  with  which  we  are  most  familiar 
consist  of  at  least  three  kinds  of 
parts,  namely,  roots,  stems,  and  leaves 
(Fig.  4). 

1 .  Name  and  describe  as  to  color  and 

form  the  parts  of  the  plant  that 
grew  beneath  the  ground. 

2.  How  does  the  stem  differ  from  the 

root  as  to  color  and  direction  of 
growth?  What  parts  of  the 
plant  above  ground  are  attached 
to  the  stem? 

3.  How  does  the  main  part  of  the  leaf 

differ  in  form  from  the  root  or 
the  stem? 

4.  Make  a  drawing,  natural  size,  of  the 

plant  you  are  studying,  labeling 
ground  level,  roots,  stem,  leaf. 

5.  On  the  plants  used  for  demonstra- 

tion, what  parts  besides  those 
named  above  do  you  find  ?  How 
do  the  colors  of  these  parts  differ 
from  the  color  of  the  rest  of  the 
plant? 
26 


FIG.  4.  —  Roots,  stems, 
leaves,  flowers,  and  fruits 
of  a  buttercup  plant. 


THE  STRUCTURE  OF  PLANTS  27 

39.  Organs  and  functions.  —  From  our  laboratory  study 
we  have  learned  that  a  common  plant  consists  of  roots,  stems, 
and  leaves,  and  that  at  certain  seasons  of  the  year  flowers 
and  fruits  are  present.     To  each  of  these  various  parts  is 
given  the  name  organ.     Roots  are  useful  to  a  plant,  for  one 
thing,  because  they  hold  it  in  the  ground,  while  stems  support 
the  leaves,  flowers,  and  fruits.     In  fact  every  organ  of  a 
plant  has  some  work  to  do,  and  this  work  is  called  its  func- 
tion.    Hence,  we  may  define  an  organ  as  a  part  of  a  plant  that 
has  a  certain  function  or  functions  to  perform. 

40.  Microscopic  structure  of  plants.  —  When  one  exam- 
ines by  the  aid  of  a  compound  microscope  a  small  portion 
of  any  of  the  organs  of  common  plants,  one  finds  that  each 
organ  is  composed  of  many  smaller  portions  too  minute  to  be 
seen  with  the  unaided  eye.     These  tiny  divisions  are  called 
cells.     We  shall  now  attempt  to  become  familiar  by  the  use 
of  the  compound  microscope  with  the  appearance  of  several 
kinds  of  plant  cells. 

41.  Study  of  plant  cells.  —  Laboratory  Study  No.  21. 

Materials:  (1)  Slides  prepared  as  follows :  Cut  a  layer  of  an  onion 
bulb  into  small  squares,  and  strip  off  from  the  inner  surface  of  each 
square  a  very  thin  layer.  Place  it  on  a  glass  slide  and  add  a  drop 
of  water.  (If  it  is  desirable  to  keep  the  slides  for  several  hours, 
put  glycerin  diluted  with  water  over  the  onion  cells.)  Cover  each 
thin  membrane  with  a  cover  glass.1  (2)  Prepared  or  freshly  cut 
thin  sections  of  roots,  stems,  and  leaves. 

1.  By  the  aid  of  the  low  power  of  the  compound  microscope, 
examine  the  slide  prepared  as  directed  in  (1)  under 
materials.  Note  that  the  thin  membrane  is  com- 
posed of  a  large  number  of  tiny  spaces  each  in- 

1  The  authors  are  indebted  to  Miss  Elsie  M.  Kupfer,  Head  of 
Department  of  Biology  of  Wadleigh  High  School,  New  York  City, 
for  suggesting  this  admirable  material  for  cell  study. 


28  PLANT  BIOLOGY 

closed  by  lines  more  or  less  dark  in  color  called 
cell-walls.  (These  parts  are  usually  seen  more  clearly 
if  the  light  is  largely  excluded  by  closing  the  dia- 
phragm in  the  stage.) 

a.  Describe  the  general  appearance  of  the  membrane, 
stating  of  what  it  is  composed. 

6.  State  whether  or  not  the  cells  in  the  various  parts  of 
the  membrane  differ  in  size  and  shape. 

2.  The  cell-wall  incloses  a  semifluid  substance  which  makes 

up  the  cell-body.  Describe  the  appearance  of  the 
cell-body. 

3.  Within  the  cell-body,  often  near  the  center  of  the  cell, 

is  usually  a  tiny  object  called  the  nucleus.  Describe 
the  location,  shape,  and  color  of  the  nucleus. 

4.  Make  a  drawing  of  three  or  four  adjacent  cells,  several 

times  as  large  as  they  appear  under  the  microscope. 
Label  cell-wall,  cell-body,  cell-nucleus. 

5.  (Demonstration.)     Secure  some  growing  sprays  of  Elodea 

(a  common  water  plant) .  Pull  off  one  of  the  youngest 
leaves  near  the  tip  end,  put  it  on  a 
slide  with  a  drop  of  water,  and  cover 
with  a  cover  glass.  Let  the  prepara- 
tion stand  in  a  warm  place  for  a  time. 
Examine  with  the  high  power  the  cells  of 

which  this  leaf  is  composed. 
Within  each  cell  note  some  green  bodies 
called  chlorophyll  bodies  (from  Greek, 
meaning  leaf  green).     These  are  the 
bodies  which  aid  in  starch  manufac- 
ture in  green  leaves.     (See  31.) 
FlG-5-1~^lodea         a.   Describe  the   form,  color,  and  use   of 

chlorophyll  bodies. 

6.  Carefully  watch  the  chlorophyll  bodies  in  several 
cells  and  describe  any  movements  you  see.  These 
movements  show  that  the  substance  of  the  cell  is 
in  motion,  and  is  carrying  the  chlorophyll  bodies 
along  with  it. 

c.  Make  a  drawing  at  least  2  inches  long  of  one  of  the 
cells  with  its  chlorophyll  bodies.  Label  cell-wall, 


THE  STRUCTURE  OF  PLANTS 


29 


protoplasm 
of  cell-body 


cell-nucleus 


cell- 
wall 


chlorophyll  bodies,  and  show  by  arrows  the  direction 
of  their  movements. 

6.  (Demonstration.)  Examine  with  the  low  power  of  the 
microscope  the  sections  of  root,  stem,  and  leaf,  or 
study  Figures  11, 12, 15,  22.  Write  a  paragraph  on 
the  microscopic  structure  of  root,  stem,  and  leaf. 

(Optional.)     Make  a  drawing  of   four  or  five  cells  from 
each  of  the  organs  studied. 

42.  Cells  and  protoplasm.  —  Under  the  microscope  cells 
at  first  appear  to  be  only  plane  surfaces  surrounded  by  lines. 
In  reality,  however,  each  cell  has 
not  only  length  and  breadth,  but 
also  thickness,  and  each  cell  is 
covered  on  all  sides  by  a  cell-wall 
which  is  composed  of  a  lifeless 
substance  known  as  cellulose. 
This  wall  is  often  so  transparent 
that  we  can  look  through  it  and 
see  the  cell-body  and  nucleus 
within  (Fig.  6). 

The  discovery  of  these  minute 
bodies  of  which  organs  are  com- 
posed was  not  made  until  about 
the  middle  of  the  last  century 
(1848).  With  the  rather  imper- 
fect microscopes  then  in  use  the 
two  discoverers,  Schleiden  and 
Schwann,  could  see  the  cell-walls 
only,  and  they  did  not  know,  as 
we  now  know,  that  the  most  im- 
portant part  of  the  cell  is  not  the  lifeless  wall  of  cellulose, 
but  the  living  substance  which  is  found  inside  the  cell -wall, 
making  up  a  large  part  of  the  cell-body  and  cell-nucleus. 


FIG.  6.  —  Plant  cell.  The  spaces 
in  the  cell-body  are  filled  with 
cell-sap. 


30  PLANT  BIOLOGY 

To  this  substance  is  given  the  name  protoplasm.  We  know 
now  that  the  living  substance  or  protoplasm  is  the  essential 
part,  while  the  wall  may  be  missing,  so  that  in  such  a 
case  there  is  no  resemblance  to  a  cell  or  box.  Biologists 
now  understand  a  cell  to  be  a  bit  of  protoplasm  (cell-body)  con- 
taining a  nucleus  (which  is  a  denser  portion  of  the  protoplasm). 

Protoplasm,  when  examined  with  the  highest  powers  of  the 
microscope,  appears  as  a  colorless,  semifluid  substance,  in 
which  are  often  seen  solid  particles  or  granules,  which  are 
probably  little  masses  of  food.  The  nucleus,  as  already 
stated,  is  commonly  found  near  the  center  of  the  cell,  and  is 
composed  of  protoplasm  denser  than  the  protoplasm  of  the 
body  of  the  cell.  The  appearance  and  composition  of  the 
protoplasm  may  be  well  represented  by  raw  white  of  egg ;  but 
in  making  this  comparison  one  should  bear  in  mind  that  the 
white  of  an  egg  is  not  living  substance. 

Within  the  cell,  too,  and  occupying  some  of  the  space  out- 
side the  nucleus,  especially  in  plant  cells,  is  cell-sap,  which  is  a 
lifeless  fluid  composed  of  water  in  which  are  dissolved  the  food 
substances  (such  as  sugar  and  mineral  matters)  used  by  cells 
in  their  growth  and  repair,  and  in  the  various  kinds  of  work 
which  they  carry  on  (Fig.  6). 

43.  Assimilation,  growth,  and  cell  division.  —  To  make 
protoplasm  the  plant  must  have  proteins,  water,  and  addi- 
tional compounds  containing  iron,  calcium,  and  several  other 
chemical  elements.  But  only  protoplasm  has  the  power  to 
combine  these  compounds  in  such  a  way  as  to  form  living 
matter.  Bearing  in  mind  the  facts  we  learned  in  studying 
food  manufacture  (33  and  34),  we  see  that  the  plant  begins 
with  simple  substances,  water  and  carbon  dioxid,  and  manu- 
factures a  more  complex  substance,  sugar.  It  uses  this  and 
other  substances  to  make  a  still  more  complex  substance, 


THE  STRUCTURE  OF  PLANTS 


31 


protein,  and  finally  ends  by  making  the  most  complex  of  all, 
protoplasm.  But,  except  in  rare  cases,  all  plants  must  have 
compounds  to  start  with ;  they  cannot  make  any  of  these 
nutrients  or  protoplasm  from  chemical  elements. 

And  thus  we  learn  that  food  materials  are  gradually 
changed  by  protoplasm  into  living  substance  like  itself.  To 
this  process  is 
given  the  name 
assimilation 
(Latin,  ad  =  to 
= similis =like) . 
As  a  result 
of  the  process 
of  assimilation 
the  amount  of 
protoplasm  of 
course  increases 


B  C 

FIG.  7.  —  Cell  division. 

ool          A>  cel1  before  division;   B,  cell  with  divided  nucleus;   C,  single 
cell  that  has  divided  into  two  cells. 

grows.     Were 

this  process  to  continue  indefinitely,  cells  would  become 
large  in  size.  This,  however,  does  not  occur;  for  when 
a  cell  reaches  its  normal  size,  the  nucleus  divides,  and  the 
halves  separate  from  each  other  to  form  two  nuclei.  The 
cell-body  now  divides  into  two  parts,  and  cell-walls  are 
formed  between  the  two  cells  (Fig.  7).  Thus  are  produced 
two  cells,  each  having  its  own  nucleus,  and  these  in  turn  as- 
similate, grow,  and  divide.  In  this  way  the  number  of  cells 
increases  with  the  growth  of  the  plant. 


CHAPTER   IV 

OSMOSIS   AND   DIGESTION 


Materials :  Four  thistle  tubes,  four  wide-mouthed  bottles ;  honey, 
molasses,  or  a  thick  solution  of  grape  sugar;  starch  (arrowroot  if 
possible),  diastase ;  white  of  egg,  peptone ;  iodine,  Fehling's  solution, 
nitric  acid.  Procure  the  intestines  of  calf  or  beef,  wash  them  thor- 
oughly inside  and  out,  and  inflate  them  by  the  aid  of  a  glass  tube. 
Tie  at  intervals  of  two  or  three  feet,  and  allow  this  animal  mem- 
brane to  dry.  Cut  off  pieces  about  two  inches  long,  and  slit  open 
each  of  the  pieces  thus  obtained.  Membrane 
prepared  in  this  way  may  be  kept  in  closed 
bottles  for  years.  If  desired,  the  pieces  of 
membrane  may 'be  used  at  once  without  dry- 
ing. Sausage  coverings  that  have  been  pre- 
served in  salt  may  be  thoroughly  washed, 
dried,  and  used. 

Thistle  tube  No.  1.  —  Hold  one  of  the  thistle 
tubes  upright,  closing  the  smaller  end  by  press- 
ing on  it  with  the  thumb.  Into  the  larger 
end  pour  the  honey,  molasses,  or  grape  sugar 
solution,  which  has  been  sufficiently  warmed  to 
pour  easily.  Half  fill  the  tube  and  nearly  fill 
the  bulb.  Moisten  one  of  the  pieces  of  intestine 
and  tie  it  tightly  over  the  bulb  of  the  thistle 
tube  so  that  none  of  the  liquid  can  escape. 
Wash  off  any  of  the  liquid  from  the  outside  of 
the  membrane,  then  dry  it  with  a  blotter,  and 
hold  the  thistle  tube  bulb  down  for  several  minutes  to  make  sure 
that  the  grape  sugar  solution  does  not  leak  out.  Now  stand  the 

32 


FIG.  8.  —  Apparatus 
for  thistle  tube 
No.  1  in  osmosis 
experiment. 


OSMOSIS  AND  DIGESTION  33 

tube,  membrane  down,  in  one  of  the  wide-mouthed  bottles  and  fill 
it  with  water  up  to  the  neck.  Add  grape  sugar  solution  to  the  thistle 
tube  until  the  level  of  the  water  in  the  bottle  and  that  of  the 
liquid  in  the  thistle  tube  is  the  same.  Connect  a  long  piece  of 
glass  tubing  to  the  upper  end  of  the  inverted  thistle  tube,  and 
support  this  tube  in  a  vertical  position,  so  that  the  membrane  does 
not  touch  the  bottom  of  the  bottle  (Fig.  8). 

Thistle  tube  No.  2.  —  Set  up  a  control  experiment  exactly  like 
No.  1,  except  that  water  should  be  put  into  the  thistle  tube  as  well 
as  in  the  bottle. 

44.  Will  water  pass  through  a  membrane  ?  —  Laboratory 
Study  No.  22. 

1.  Give  in  your  own  words  a  description  of  the  way  thistle 

tube  No.  1  was  prepared,  making  a  diagram  of  the 
apparatus,  and  labeling  level  of  water  in  bottle 
and  of  grape  sugar  solution  in  thistle  tube  at  the 
beginning  of  the  experiment. 

2.  At  the  end  of  a  few  hours  compare  the  level  of  the  liquid 

in  thistle  tube  No.  1  with  the  level  in  thistle  tube 
No.  2. 

a.  How  many  inches  has  the  grape  sugar  risen  in  No.  1  ? 

b.  Is  there  a  similar  rise  in  the  water  in  thistle  tube 

No.  2? 

c.  What  must  have  passed  into  thistle  tube  No.  1  to 

cause  the  liquid  to  rise? 

d.  Through  what  must  this  liquid  have  passed  to  get 

into  the  thistle  tube? 

3.  Do  you  conclude,  therefore,  that  water  will  or  will  not 

pass  through  a  membrane  ? 

45.  Will  grape  sugar  pass  through  a  membrane?  —  Labor- 
atory Study  No.  23. 

1.  At  the  end  of  a  few  hours  test  the  liquid  in  bottle  No.  1 
by  putting  a  glass  tube  to  the  bottom  of  the  bottle, 
pressing  the  thumb  over  the  top  of  the  tube,  and 
removing  the  sample  of  liquid  thus  obtained  to  a 
clean  test  tube;  add  Fehling's  solution  and  boil. 


PLANT  BIOLOGY 


a.  Describe  what  was  done. 

b.  Is  grape  sugar  present  now?     How  do  you  know? 

c.  What  must  have  happened  to  produce  this  result? 

2.  We  have  now  proved  that  two  different  liquids  have 

passed  through  the  membrane. 

a.   Name  these  two  liquids. 

6.    Which  of  these  two  liquids  has  passed  through  the  mem- 
brane in  the  greater  quantity  ?     How  do  you  know  ? 

c.  Which  of  these  two  liquids  is  the  thicker  or  denser? 

d.  By  a  great  many  experiments  it  has  been  proved  that, 

when  any  two  liquids  of  different  density  are  sep- 
arated by  a  plant  or  animal  membrane,  results  sim- 
ilar to  those  noted  above  follow.  To  this  inter- 
change of  liquids  is  given  the  name  osmosis.  In  this 
process  of  osmosis,  is  the  greater  flow  of  liquid  from 
the  less  dense  to  the  more  dense,  or  from  the  more 
dense  to  the  less  dense? 

e.  Why  did  not  the  water  rise  in  thistle  tube  No.  2  ? 

3.  Do  you  conclude,  therefore,  that  grape  sugar  will  or  will 

not  pass  through  a  membrane? 

46.    Osmosis  in  living  cells.  —  Laboratory  Study  No.  24. 
Peel  a  potato  and  then  cut  several  cross  sections  about 


inch  in  thickness. 


FIG.  9.  —  Cells  from  a 
potato,  showing  cell- 
walls,  cell-sap,  and 
starch  grains  of  differ- 
ent sizes. 


Allow  these  sections  to  stand  in  the 
air  until  they  bend  readily.  Half  fill 
one  tumbler  with  water  and  a  second 
tumbler  with  a  strong  solution  of 
sugar  or  salt.  Place  some  of  the 
sections  in  each  of  the  two  tumblers 
and  leave  them  for  several  hours. 

1.  Describe  the  preparation  of  this 

experiment. 

2.  Remove  a  section  of  potato  from 

each  of  the  liquids  and  bend 
them.  Compare  the  change  that 
has  taken  place  in  the  rigidity  or 
stiffness  of  the  sections  placed 


in  the  strong  solution  and  those  in  the  tap  water. 


OSMOSIS  AND  DIGESTION  35 

4.  Potato  sections,  like  those  of  all  parts  of  living  plants, 
are  composed  of  a  large  number  of  living  cells,  each  one 
inclosed  by  a  cell  membrane  (Fig.  9). 
Call  to  mind  what  you  learned  in  45,  and  state  why  the 
cells  become  even  more  flabby  in  one  solution  and  more 
rigid  in  the  other. 

47.  Will  starch  pass  through  a  membrane?  —  Laboratory 
Study  No.  25. 

Thistle  tube  No.  3.  —  Put  into  a  third  thistle  tube  a  mixture  of 
starch  and  water,  cover  the  bulb  with  a  membrane,  and  invert  in  a 
bottle  of  water,  as  already  directed  for  the  first  thistle  tube.  See 
that  the  level  of  the  liquid  is  the  same  in  all  of  the  experiments. 

1.  In  what  respects  does  the  preparation  of  thistle  tube 

No  3  resemble  that  of  No.  1?  How  do  the  two 
experiments  differ? 

2.  At  the  end  of  a  few  hours  test  the  liquid  in  bottle  No.  3 

by  removing  a  sample  to  a  test  tube  (as  already 
directed  in  45),  and  adding  iodine  solution. 

a.   Is  starch  present?     How  do  you  know? 

6.  What  is  your  conclusion  as  to  the  possibility  of  starch 
passing  through  a  membrane? 

3.  What  have  these  experiments  in  osmosis  taught  you  as 

to  one  difference  between  starch  and  grape  sugar? 

48.  Definitions  and  applications.  —  The  experiments  we 
have  been  performing  have  most  important  relations  to  the 
study  of  all  living  plants  and  animals.     We  may  give  the 
following  as  a  definition  of  the  process  we  are  considering : 
Osmosis  is  the  interchange  of  liquids  of  different  density  that  are 
separated  by  a  plant  or  an  animal  membrane,  and  in  this  pro- 
cess the  greater  flow  is  always  from  the  less  dense  to  the  more 
dense. 

We  shall  constantly  refer  to  this  principle  of  osmosis,  and 
we  shall  find  that  it  explains  in  large  measure  the  absorption 
of  soil  water  by  roots,  the  transfer  of  sap  from  one  part  of  a 


36  PLANT  BIOLOGY 

plant  to  another,  as  well  as  the  processes  by  which  the  blood 
of  animals  obtains  and  gives  off  food  to  various  cells  of  the 
body. 

By  the  preceding  experiments  we  have  proved  that  there  are 
two  classes  of  food  substances.  One  kind  (including  water  and 
grape  sugar)  will  readily  pass  through  a  membrane  by  osmosis ; 
the  other  kind  (represented  by  starch)  will  not.  In  our  study 
of  cells  we  learned  that  the  protoplasm  or  living  substance  is 
inclosed  by  a  cell-wall  which  separates  one  cell  from  another. 
Now  if  cells  are  to  make  use  of  the  food  materials  manufac- 
tured in  other  parts  of  the  plant,  each  food  substance  must  be 
in  such  a  form  that  it  can  pass  through  these  cell-membranes. 
It  is  evident  that  water  and  grape  sugar  can  .do  this.  We 
find,  however,  large  quantities  of  starch  stored  in  cells 
(Fig.  9).  Hence,  to  be  available  for  use  in  other  cells,  some 
change  must  be  made  in  this  food  substance  before  it 
can  be  transferred  from  cell  to  cell.  We  shall  now  show  by 
experiment  what  this  change  is. 

49.    How  starch  is  made  ready  to  pass  through  a  membrane. 

-  Laboratory  Study  No.  26. 

Into  each  of  two  test  tubes  put  a  small  amount  of  starch 
(arrowroot- starch  if  it  can  be  obtained),  add  some  water, 
shake,  and  boil.  To  the  starch  mixture  in  one  test  tube  add 
some  diastase,  equal  in  amount  to  one-half  the  size  of  a  pea. 
(Diastase  is  a  chemical  substance  produced  or  secreted  by 
the  protoplasm  of  plant  cells.)  Put  the  two  test  tubes  side 
by  side  in  a  warm  place  for  5  minutes  if  arrowroot  starch, 
24  hours  if  corn  starch  is  used,  then  test  a  small  amount  of 
the  mixture  in  each  test  tube  by  adding  a  few  drops  of  iodine. 

1.  Describe  in  your  own  words  what  has  been  done. 

2.  In  which  test  tube  do  you  find  starch  present  ? 

3.  Now  test  with  Fehling's  solution  a  small  quantity  of 

each  mixture.     In  which  tube  do  you  find  grape  sugar  ? 


OSMOSIS  AND  DIGESTION  37 

4.  What  do  you  conclude,  therefore,  as  to  the  effect  of  dias- 

tase on  starch? 

5.  Why  is  this  change  necessary  if  starch  is  to  be  used  by 

plants  ? 

50.  To  prove  that  starch  is  made  soluble  in  growing  plants. 

—  Laboratory  Study  No.  27. 

1.  Pound  two  or  three  corn  grains  into  a  powder  and  put 

some  of  this  corn  meal  into  a  test  tube,  add  water,  and 
boil.  To  one-half  of  the  mixture  add  iodine,  and  to  the 
other  half,  Fehling's  solution,  and  boil.  Give  a  careful 
description  of  the  experiment  and  state  your  observa- 
tions and  conclusions. 

2.  Secure  some  germinating  corn  grains,  cut  them  into  small 

pieces,  and  test  some  of  them  with  Fehling's  solution  as 
in  1  above.  Describe  the  experiment,  stating  your  ob- 
servations and  conclusions. 

3.  The  change  in  starch  that  you  have  described  is  known 

as  digestion.  What  reason  have  you  for  believing  that 
digestion  of  starch  takes  place  when  corn  grains  ger- 
minate ? 

51.  Definition  of  digestion.  —  We  may  define  digestion  as 
the  chemical  change  whereby  insoluble  food  substances  are  made 
ready  to  pass  through  membranes  and  become  ready  for  the  use 
of  protoplasm.     Let  us  now  by  experiment  determine  whether 
or  not  protein  needs  digestion. 

52.  Will  protein  pass  through  a  membrane?  —  Laboratory 
Study  No.  28. 

Thistle  tube  No.  4-  —  Secure  some  white  of  egg,  cut  it  with  scis- 
sors and  mix  it  with  water.  (White  of  egg,  we  found,  contains  a 
large  amount  of  protein.)  Prepare  the  fourth  thistle  tube  in  the 
same  way  as  directed  for  thistle  tube  No.  1 ,  only  using  white  of  egg 
and  water  instead  of  grape  sugar.  See  that  the  level  of  the  liquid 
is  the  same  as  in  thistle  tube  No.  2. 


38  PLANT  BIOLOGY 

1.  In  what  respects  does  the  preparation  of  thistle  tube 

No.  4  resemble  that  of  thistle  tube  No.  1  ?  How  do  the 
two  experiments  differ  ? 

2.  Allow  the  experiment  to  stand  for  several  hours,  and  then 

remove  with  a  glass  tube  a  sample  of  the  liquid  in 
bottle  No.  4,  and  test  it  by  adding  nitric  acid  and  boil- 
ing. Is  protein  present  ?  How  do  you  know  ? 

3.  Do  you  conclude,  therefore,  that  protein  will  or  will  not 

pass  through  a  membrane  ? 

53.  Digestive  ferments.  —  We  have  stated  that  proto- 
plasm secretes  a  substance  called  diastase,  and  have  shown 
that  this  diastase  will  change  insoluble  starch  to  soluble  grape 
sugar,  which  will  pass  from  one  cell  to  another  by  the  process 
of  osmosis.  Diastase  is  a  substance  known  as  a  digestive 
ferment.  Now  protoplasm  produces  other  digestive  ferments, 
some  of  which  will  change  insoluble  protein  to  a  soluble  sub- 
stance known  as  peptone.  The  latter  will  readily  pass  by  the 
process  of  osmosis  through  a  membrane. 

Fats,  also,  like  starch  and  protein,  are  insoluble  and  can- 
not, therefore,  pass  by  osmosis  through  cell  walls.  To  make 
these  food  substances  available  for  use  they  must  also  be 
changed  by  the  plant  cells  into  such  forms  that  they  may  be 
readily  transferred  from  one  part  of  the  plant  to  another. 
These  changes  are  caused  by  other  chemical  ferments  pro- 
duced by  protoplasm. 


CHAPTER  V 
ADAPTATIONS   OF  THE  NUTRITIVE  ORGANS   OF  PLANTS 

54.  The  nutritive  organs  of  plants.  —  From  our  study  of 
food  manufacture  (29-34)  we  learned  that  the  plant  foods  are 
produced  in  green  leaves.     Before  this  process  of  food  manu- 
facture can  go  on,  however,  the  cells  in  the  leaf  must  be  sup- 
plied with  raw   materials  from  the  air   and  from  the  soil. 
Since  the  roots,  stems,  and  leaves  are  all  concerned  in  food 
making,  these  organs  are  known  as  the  nutritive  organs  of 
plants.     Each  of  these  organs  has  several  functions ;  we  shall 
now  learn  what  some  of  these  functions  are,  and  how  the 
nutritive  organs  are  adapted  for  the  work  they  do. 

I.    THE  STRUCTURE  AND  ADAPTATIONS  OF  ROOTS 

55.  The  structure  of  roots.  —  Laboratory  Study  No.  29. 
A.   Gross  structure  of  roots. 

Select  the  largest  roots  of  a  well-developed  seedling  or  the 
roots  of  common  weeds.  By  means  of  your  thumb  and  finger 
nail  gently  scrape  off  the  outer  layers  from  a  piece  of  one  of 
these  roots.  When  no  more  of  the  material  can  be  easily 
removed  by  this  method,  pick  to  pieces  the  central  part  of 
the  root  which  is  left.  The  outer  layer  you  have  removed  is 
largely  composed  of  the  cells  of  the  cortex,  and  the  central 
part  that  has  been  exposed  is  called  the  central  cylinder. 

1.  Tell  what  you  have  done. 

2.  Which  is  composed  of  the  tougher  and  harder  material, 

the  cortex  or  the  central  cylinder  ? 
39 


40  PLANT  BIOLOGY 

3.  Make  a  diagram  greatly  enlarged  of  a  piece  of  root 
prepared  as  directed  above.  Label  cortex,  central 
cylinder,  fibers  of  central  cylinder. 

B.  Root-hairs. 

Note  to  the  Teacher.  —  Root-hairs  may  be  grown  for  study  as 
follows :  Cover  the  bottom  of  as  many  Petri  dishes  as  are  needed 
with  a  layer  of  blue  blotting  paper.  Soak  the  paper  with  water  and 
lay  several  grains  of  soaked  barley,  oats,  or  corn  upon  the  bottom 
of  each  dish.  Put  ttte  covered  dishes  in  a  warm  place  for  several 
days.  When  the  root- hairs  have  developed,  wipe  the  moisture  from 
the  inside  of  the  covers,  quickly  replacing  the  latter.  If  Petri  dishes 
are  not  available,  two  clean  glasses  of  any  convenient  size  may  be 
used  instead.  Cover  one  of  the  plates  with  layers  of  wet  blotting 
paper,  put  the  soaked  grains  in  position,  and  cover  with  the  second 
glass,  fastening  the  two  together  with  threads  or  strings.  Stand 
one  end  of  the  preparation  thus  made  in  a  jar  with  enough  water  to 
reach  the  lower  edge  of  the  blotting  paper. 

Examine  first  with  the  naked  eye  and  then  with  a  hand 
magnifier  the  roots  of  sprouted  grains,  developed  as  described 
above.  Notice  tiny  outgrowths  from  the  sides  of  the  roots; 
these  outgrowths  are  called  root-hairs. 

1.  Look  at  the  very  tip  of  the  root  and  state  whether 

root  hairs  are  there  present  or  absent. 

2.  State  whether  the  root-hairs  are  longest  near  the  tip 

or  in  the  direction  of  the  grain. 

3.  Make  a  drawing  much  enlarged  to  show  the  shape  of 

one  of  the  roots  including  the  root-tip  and  the 
various  lengths  of  root-hairs.  Label  root-tip,  root- 
hairs. 

C.  Microscopical  structure  of  the  tip  of  a  root.     (Optional.) 

Examine  with  the  aid  of  the  low  power  of  the  compound  micro- 
scope a  root- tip  mounted  on  a  slide  in  drop  of  water  and  covered 
with  a  cover  glass.  Make  a  sketch  very  much  enlarged  to 
show  — 


THE  NUTRITIVE  ORGANS  OF  PLANTS  41 

1.  The  outline  of  the  root  including  the  tip. 

2.  A  loose  mass  of  cells  covering  the  lower  end  of  the  root  which 

make  up  the  root<-cap. 

3.  Label  root- tip,  cells  of  the  root- cap. 

56.    The  functions  of  roots.  —  Laboratory  Study  No.  30. 

A.  Roots  as  organs  for  holding  the  plant  to  the  soil. 

Secure  a  vigorously  growing  plant  in  a  pot  (e.g.  a  rubber 
plant)  or  better  try  the  following  experiment  on  a 
good  sized  weed  in  a  field.  Attach  to  the  stem  just 
above  ground  level  a  spring  balance.  Pull  on  the 
balance  until  the  plant  shows  signs  of  letting  go  its 
hold  on  the  soil,  then  note  the  reading  in  pounds  on 
the  scale. 

1.  In  your  own  words  describe  what  was  done. 

2.  How  much   force    in   pounds   was   exerted   on   the 

plant? 

3.  What  important  function  of  roots  is  shown  by  this 

experiment  ? 

B.  Roots  as  organs  for  absorbing  soil-water. 

(Before  proceeding  further  with  the  root  study,  the  osmo- 
sis experiments,  44-53,  should  be  performed  if  they 
have  not  already  been  done.) 

Study  the  diagram  of  a  root-hair  in  the  text-book  (Fig.  12) 
and  if  possible  examine  with  the  low  power  of  the 
microscope  some  of  the  younger  (shorter)  root- 
hairs.  Each  root-hair  is  an  elongated  part  of  an 
outer  cell  of  the  root. 

1.  Draw  in  your  note-book  a  diagram  of  a  root-hair, 

labeling  cell-wall,  thin  layer  of  protoplasm,  cell- 
sap,  and  nucleus. 

2.  What   separates   the    soil-water   from  the   cell-con- 

tents? 

3.  Recall   the   characteristics   of   cellular   structure   as 

given  in  42.     Now  state  which  is  the  more  dense,  the 
soil-water  or  the  cell-contents. 


42  PLANT  BIOL9GY 

4.  In  which  direction,  therefore,  will  there  be  the  greater 

movement  of  liquid  in  the  process  of  osmosis  ? 

5.  How,  then,  is  a  root-hair  adapted  by  structure  for 

absorbing  soil-water? 

C.  Roots  as  organs  for  transmitting  soil-water. 

Place  some  seedlings  or  weeds  in  red  ink  so  that  only  the 
lower  ends  of  the  roots  are  in  the  liquid.  Cut  some 
cross  sections  of  these  roots  above  the  point  where 
they  were  in  contact  with  the  ink.  Examine  the 
cross  section  of  the  root  prepared  in  this  way. 

1.  Describe  the  experiment  as  it  was  performed. 

2.  Through  what  part  of  the  root   (cortex  or  central 

cylinder)  has  most  of  the  liquid  passed?  How  do 
you  know? 

3.  Make  a  sketch  about  an  inch  in  diameter  of  the  cross 

section  of  the  root,  to  show  the  colored  and  colorless 
portions.  Label :  part  of  the  root  through  which 
liquid  traveled,  unstained  portion  of  root,  cortex, 
central  cylinder. 

D.  Roots  as  organs  for  the  storage  of  food. 

Cut  some  slices  about  an  inch  thick  from  parsnips  or  other 
fleshy  roots,  and  divide  each  slice  vertically  in 
halves.  Put  the  pieces  in  water  and  boil  for  a  few 
moments  to  partially  cook  them.  Pour  iodine 
solution  over  some  of  the  pieces;  to  others  add 
strong  nitric  acid ;  boil  still  other  pieces  in  a  test 
tube  with  Fehling's  solution. 

1.  Describe  the  preparation  of  each  of  the  experiments, 

and  state  in  each  case  your  observations. 

2.  What  do  you  conclude  as  to  the  presence  or  absence  of 

each  of  three  of  the  food  substances  in  various  parts 
of  the  fleshy  root  you  are  studying  ? 

3.  What  function  of  roots  do  these  experiments  demon- 

strate ? 

57.    Adaptations  of  roots  for  holding  to  the   soil.  —  One 

of  the  most  obvious  functions  of  roots  is  that  of  holding  plants 
firmly  in  the  ground.     If  the  soil  is  carefully  removed  from 


THE  NUTRITIVE  ORGANS   OF  PLANTS 


43 


the  roots  of  a  weed  or  a  tree,  these  roots  will  be  found  to 
extend  outward  in  all  directions  to  a  distance  even  greater 
than  do  the  branches  above  ground.  When  one  remembers 
the  tremendous  force  exerted  upon  trees  by  high  winds,  the 
necessity  for  this  extensive  root  anchorage  will  be  evident. 
In  our  dissection  of  the  root  even  of  a  young  plant  we  found 


FIG.  10.  —  Roots  of  a  tree,  showing  method  of  transplanting  a  large  tree. 
(Courtesy  of  Isaac  Hicks  and  Sons,  Westbury,  Long  Island.) 

that  the  central  cylinder  was  composed  of  tough  fibers  which 
are  made  up  of  elongated  wood-cells  (similar  to  those  shown 
in  Fig.  15).  As  a  plant  grows  older,  these  central  cylinders 
become  so  thick  and  tough  that  they  will  resist  an  enormous 
strain  without  breaking. 

58.  Adaptations  of  roots  for  absorbing  and  transmitting 
soil-water.  —  A  second  function  of  roots  we  found  to  be  that 
of  absorbing  soil-water  and  transmitting  it  to  the  stem.  The 


PLANT  BIOLOGY 


whole  outer  surface  of  young  roots  is  covered  with  a  single 
layer  of  thin-walled  cells  which  form  the  epidermis.  Many  of 
these  cells  develop  tubular  outgrowths  known  as  root-hairs 


. 

£*&      •    :  /Ulx/Mx 


?«*m 


FIG.    11.  —  Cross    section    of    root,  FIG.  12.  —  Diagram   of   a  lengthwise 

showing  root-hairs  and  epidermis  section     of     two     root-hairs    with 

cells  on  the  outer  surface,  cells  of  adjacent     cells    of    the  epidermis, 

cortex  within,  and  woody  central  and  with  two  cells  of  the  cortex, 
cylinder  with  its  ducts.  —  (Bailey.) 

(see  56,  B).  By  studying  Fig.  12  it  will  be  evident  that  each 
root-hair  consists  of  a  cell-wall  lined  by  a  thin  layer  of 
protoplasm.  The  interior  of  the  cell  is  largely  filled  with 

cell-sap.  On  the  outside 
of  each  root-hair  is  soil- 
water.  All  the  conditions 
necessary  for  osmosis  are 

FIG.  13.  —  Portion  of  a  root-hair  with  ad- 
hering particles  of  soil.  —  (Strasburger.) 

which  separates  the  soil-water  from  the  denser  cell-sap/ 
From  the  law  of  osmosis,  we  should  expect  a  flow  of  liquids 
in  both  directions,  the  greater  flow  being  into  the  cell-sap 
from  the  soil-water.  It  has  been  found,  however,  that  the 


therefore    present.     The 

cell-wall  IS  the  membrane 


THE  NUTRITIVE  ORGANS  OF  PLANTS 


45 


protoplasm  permits  the  inward  flow 
of  the  soil-water,  but  practically 
prevents  the  outward  flow  of  the 
cell-sap.  Thus  we  see  that  proto- 
plasm has  a  selective  action.  Since 
the  growing  parts  of  roots  have 
countless  root-hairs,  these  cells  of 
the  epidermis  together  act  like  a 
great  sponge  which  absorbs  the  large 
quantities  of  water  and  mineral  mat- 
ters which  are  needed  by  all  plants. 
This  liquid  passes  from  one  cell  to 
another  until  it  reaches  the  central 
cylinder.  A  study  of  the  micro-  FIG.  14.—  Ducts  that  convey 


scopical  structure  of  the  central  cyl-       ^he  root 

inder  makes  evident  the  fact  that       The  walls  of  these  ducts 

,  r  •  /.     ,-,  •    ,  ,          are  strengthened  by  spiral 

this  part   of   the  root  consists  not       fibers  or  rings. 
only  of  tough  wood  cells  as  explained 

in  the  preceding  section,  but  also  of  tubular  cells  called  ducts. 
(See  Fig.  14.)  Through  these  ducts  the  sap  is  conveyed  up- 
ward to  the  stem. 


II.   THE  STRUCTURE  AND  ADAPTATIONS  OF  STEMS 

59.    The  structure  of  a  woody  stem.  -—  Laboratory  Study 
No.  31. 

A.    The  structure  of  a  young  stem. 

Secure  pieces  of  a  young  stem  of  a  horse-chestnut,  maple, 
lilac,  or  other  woody  stem  that  shows  the  three 
layers  of  bark.  Split  some  pieces  lengthwise  in 
halves. 

1.  Peel  off  the  outer  covering,  the  bark,  from  a  piece  of 
the  stem  till  the  wood  is  exposed.  The  bark  of 


46  PLANT  BIOLOGY 

a  young  stem  usually  consists  of  three  more  or 
less  distinct  layers. 

a.  With  a  knife  gently  scrape  off  an  outer  or  brown 

bark,  and  expose  a  dark  green  layer  known  as  the 
green  bark.  Scrape  this  until  you  come  to  a 
more  or  less  tough  layer  known  as  the  fibrous 
bark  or  bast  (which  may  be  slightly  green). 
Describe  each  of  these  barks  as  to  position  and 
color. 

b.  Pick  into  threads  the  fibrous  bark ;  in  what  direc- 

tion of  the  stem  do  the  fibers  run?  By  break- 
ing strips  of  each  layer  determine  which  of  the 
three  barks  is  toughest. 

2.  Feel  of  the  wood  from  which  the  bark  has  just  been 

removed.  Describe  the  substance  which  covers 
the  wood,  after  scraping  off  a  little  with  your 
thumb  nail.  This  is  the  cambium  or  growing 
layer,  which  produces  the  new  wood  and  bark. 
When  the  bark  is  torn  off,  the  cells  of  this  layer 
are  broken  and  the  slimy  protoplasm  oozes  out. 

3.  By  means  of  a  penknife  or  pin  dig  into  the  wood  and 

also  into  the  pith  at  the  center  of  the  stem. 
Compare  the  wood  and  the  pith  as  to  relative 
position  and  hardness. 

4.  By  the  aid  of  compasses  make  a  diagram,  at  least  three 

inches  in  diameter,  of  the  cross  section  of  a 
woody  stem  to  show  the  relative  thickness  of 
the  various  layers.  (These  layers  might  well  be 
represented  by  different  colors.)  Label  brown 
bark,  green  bark,  fibrous  bark  or  bast,  cambium 
layer,  wood,  pith. 

B.    The  structure  of  an  older  stem.     (Optional.) 

Cut  some  cross  sections  of  stems  several  years  old.  (Ad- 
mirable material  can  be  obtained  by  sawing  into  pieces 
about  two  inches  long  white  oak  sticks  three  to  four 
inches  in  diameter.)  Each  piece  should  then  be  split 
into  halves  and  each  surface  planed  and  sandpapered. 
These  pieces  are  valuable  as  permanent  preparations. 


THE  NUTRITIVE  ORGANS  OF  PLANTS  47 

1.  Which  of  the  three  regions  (bark,  wood,  and  pith)  found  in 

the  young  stem  can  you  readily  distinguish  ?  Which 
of  the  three  becomes  very  much  thicker  and  harder  as 
the  stem  grows  older  ?  Which  is  very  small  in  quan- 
tity when  compared  with  the  young  stem  ? 

2.  The  curved  layers  of  wood  in  the  cross  section  are  known  as 

annual  rings,  so  called  because  usually  only  one  ring  is 
formed  each  year  by  the  cambium  layer.  How  many 
years  of  growth  are  shown  in  the  piece  of  wood  you 
are  studying  ? 

3.  The  lines  in  the  cross  section  extending  like  the  spokes  of  a 

wheel  are  the  pith  rays  or  medullary  rays.  Describe 
the  appearance  of  these  rays.  The  shining,  lighter 
colored  surfaces  (to  which  the  beauty  of  "quartered 
oak"  furniture  is  due),  that  appear  in  the  longitudinal 
sections  of  oak  wood,  are  the  pith  rays.  Find  pith 
rays  in  the  middle  surfaces  of  some  of  the  oak  pieces 
you  are  studying,  and  describe  them. 

4.  Make  a  Jarge  diagram  of  the  cross  section  of  the  piece  of 

wood  you  are  studying.  Label  bark,  wood,  annual 
rings,  medullary  or  pith  rays. 

60.  The  structure  of  the  corn  stem.  —  Laboratory  Study 
No.  32.  (Optional.) 

Cut  pieces  about  two  inches  in  length  from  full-grown  corn  stalks,  and 
split  each  piece  in  halves.  (If  necessary  these  pieces  may  be  preserved 
from  year  to  year  in  4  per  cent  formalin  or  in  70  per  cent  alcohol.) 

Examine  the  cross  and  longitudinal  sections  of  corn  stem.  Find 
the  rind  (the  outer  layer),  the  woody  bundles  or  fibers  (thread-like 
structures),  and  the  pith  (material  between  the  bundles). 

1.  Thrust  your  pencil  point  into  the  pith;  is  this  material  hard  or 

soft? 

2.  Pull  out  one  of  the  woody  fibers ;  is  it  tough  or  tender  ? 

3.  Push  your  pencil  point  into  the  rind ;  is  it  hard  or  soft  ? 

4.  Make  a  drawing   (X  2)   showing  both  cross  and  longitudinal 

surfaces.     Label  rind,  woody  bundles,  pith. 


48  PLANT  BIOLOGY 

61.  Experiments  to  show  the  upward  path  of  sap  through 
stems.  —  Laboratory  Study  No.  33. 

A.  Stand   some  live  twigs  (e.g.  maple  or  horse-chestnut)  in 

red  ink  for  a  day  or  two ;  cut  off  pieces  above  the 
level  of  the  ink,  and  split  some  of  these  pieces  in 
half  lengthwise. 

1.  Describe  the  preparation  of  the  experiment. 

2.  Through  what  part  of  the  stem  does  the  red  ink  rise  ? 

3.  What  do  you  conclude,  therefore,  as  to  the  part  of  a 

woody  stem  through  which  sap  rises? 

B.  (Optional.)     Stand  in  red  ink  some  pieces  of  fresh  corn  stalk 

(or  if  this  cannot  be  obtained,  some  Tradescantia  or 
any  lily  stem).  Cut  some  cross  and  longitudinal  sec- 
tions above  the  level  of  the  ink. 

1.  Write  an  account  of  the  experiment,  stating  your  observations. 

2.  In  the  stem  you  are  studying,  is  sap  carried  upward  by  the 

rind  (epidermis  in  the  lily),  or  by  the  pith,  or  by  the 
woody  fibers  ?  How  do  you  know  ? 

62.  Stems  as  organs  for  support  and  leaf  exposure.  — 

When  we  studied  the  manufacture  of  carbohydrates  by  plants, 
we  proved  that  green  leaves  must  be  exposed  to  sunlight  in 
order  to  carry  on  this  important  function.  When  the  leaves 
receive  the  proper  amount  of  exposure,  the  food  can  be 
manufactured  rapidly.  Hence,  we  should  expect  to  find  that 
leaves  are  arranged  in  such  a  way  as  to  secure  the  best 
amount  of  sunlight.  Where  plants  are  more  or  less  crowded, 
as  in  forests  or  thickets,  the  main  stems,  such  as  the  trunks  of 
trees,  usually  grow  tall,  thus  lifting  the  leaves  to  the  light. 
The  amount  of  light  exposure  of  trees  and  of  most  other  plants 
is  largely  increased  by  branches  and  their  subdividing  twigs, 
^to  which  the  leaves  are  attached. 

In  order  that  the  trunk  and  its  branches  may  be  able  to 
support  the  leaves  and  withstand  the  force  of  storms,  thick- 


THE  NUTRITIVE  OEGANS   OF  PLANTS 


49 


walled  wood-cells  are  developed.  Each  wood-cell,  when 
separated  out  from  the  rest,  and  examined  with  the  high 
power  of  the  compound  microscope,  is  seen  to  be  shaped 
somewhat  like  a  tiny  toothpick,  and  the  thin  ends  of  these 
cells  fit  together  closely  by  overlapping.  (See  Fig.  15.) 


sieve  tube  duct  duc^ 

FIG.  15.  — Woody  bundle  of  sunflower  stem. 


pith 


Stems  like  the  corn  stalk  and  bamboo  have  most  of  their  sup- 
porting material  on  the  outside,  and  these  stems  are  in  the  form  of 
cylinders  which  are  either  hollow  (as  in  grasses)  or  filled  with  pith 
through  which  pass  the  woody  bundles  (as  in  the  corn  stalk).  It 
has  been  proved  that  when  a  given  amount  of  material  is  arranged 
in  the  form  of  a  hollow  tube,  it  will  withstand  a  much  greater  strain 
without  breaking  than  when  this  material  is  in  the  form  of  a  solid 
rod.  This  mechanical  principle  is  made  use  of  in  the  construction 
of  the  frame  of  a  bicycle  and  of  the  pillars  that  support  buildings. 

63.  Stems  as  organs  for  the  transmission  of  sap.  —  Leaves 
not  only  require  an  abundance  of  sunlight,  but  they  must 


50 


PLANT  BIOLOGY 


also  be  supplied  with  water  and  other  materials  from  the 
soil.  Our  experiment  with  red  ink  (see  61)  showed  that  the 
soil-water  is  carried  upward  through  the  woody  portions  of 
stems.  A  microscopical  examination  of  thin  sections  of 
a  stem  (see  Fig.  15)  shows  the  presence  of  tubular  cells 
known  as  ducts,  similar  to  those  found  in 
the  central  cylinder  of  roots  with  which 
they  are  connected.  These  are  the 
parts  of  the  wood  through  which  the 
soil-water  passes  most  readily  up  to  the 
leaves. 

After  the  raw  materials  have  been 
changed  into  the  plant  foods  by  green 
leaves,  these  plant  foods,  by  the  process 
of  digestion,  are  changed  into  such  a 
form  that  they  can  pass  from  the  leaves 
into  the  fibrous  bark  in  which  are  tubular 
cells  known  as  sieve-tubes.  (See  Figs.  15 
and  16.)  Through  these  the  liquid  food 
FIG.  16.—  Sieve  tube,  passes  down  the  stem  to  be  stored  away 


the  leaf,  stem,  and 
root.  A,  longitu- 
dinal section  show- 
ing edge  view  of 

middle)  ;  B,  sur- 
face view  of  sieve 
plate. 


In  young  stems  the  pith  rays  or  medul- 
j  (59  B  3)   th    fi      jj        extend- 

ing  from  the  bark  toward  the  center  of 
the  stem,  are  supposed  to  serve  as  chan- 

' 

nels  for  the  passage  of  food  across  the 
stem  and  also  for  the  storage  of  food. 


In  the  type  of  stem  represented  in  the  corn,  lilies,  and  palm 
trees,  the  woody  material  through  which  sap  passes  is  not  ar- 
ranged in  the  form  of  annual  rings,  but  the  woody  bundles  are 
scattered  through  the  pith.  Each  bundle  consists  of  ducts  that 
carry  the  soil-water  up  through  the  stem  out  into  the  leaves,  of 
sieve-tubes  that  convey  downward  from  the  leaves  the  manufac- 


THE  NUTRITIVE  ORGANS  OF  PLANTS 


51 


tured  food  substances,  and  of  wood  cells  that  help  to  strengthen  the 
bundle. 

64.  Changes  in  stems  during  their  growth.  —  In  our  dis- 
cussion thus  far,  we  have  considered  the  adaptations  of  stems 
for  exposing  leaves  to  the  light  and  for  transmitting  food 
materials  to  and  from  the  leaves.  But  the  stem  has  other 
important  functions  which  we  are  now  to  consider.  In  a 
young  twig,  before  the  brown  bark  thickens  and  shuts  out 
the  light,  the  green  bark,  on  account  of  the  presence  of  chlo- 
rophyll, is  enabled  to  carry  on  the  manufacture  of  carbohy- 
drates. In  a  very  young,  stem  the  surface  is  covered  by  thin 
epidermis  which  helps  to  prevent 
the  undue  escape  of  moisture.  In 
this  layer  are  tiny  openings  that 
allow  the  inward  and  outward 
passage  of  gases  that  occur  in 
breathing  and  food  manufacture. 
Later  this  epidermis  is  replaced 
by  the  outer  or  brown  bark,  which 
serves  as  a  means  of  protection 
against  unfavorable  weather  con- 
ditions and  insects.  In  this  brown 
bark  the  tiny  openings  referred 
to  above  are  developed  into  large 
openings  known  as  lenticels  which 
carry  on  the  same  functions.  Ii>  an  old  tree  the  outer  bark 
becomes  very  thick  and  corky  and  the  green  layer  dis- 
appears entirely. 

The  growth  of  the  tree  in  thickness,  as  already  stated,  is 
due  to  the  activity  of  a  layer  of  cells  between  the  wood  and  the 
fibrous  bark.  This  is  the  cambium  layer  (Fig.  15).  In  early 
spring  the  cambium  cells  by  rapid  growth  and  division  form 
on  their  innermost  surface  a  new  layer  of  wood  (which  appears 


FIG.  17.  —  Cross  section  of  a 
tree  trunk  showing  bark, 
wood  (with  its  annual  rings 
and  medullary  rays),  and  pith 
at  center.  —  (Courtesy  of 
New  York  Botanical  Garden.) 


PLANT  BIOLOGY 


FIG.  18.  —  Cross  section  of 
young  bamboo,  showing  hard 
outer  rind,  woody  bundles, 
scattered  through  the  pith. 
The  center  of  the  stem  is 
hollow.  —  (Courtesy  of  New 
York  Botanical  Garden.) 


as  a  ring  in  cross  section),  and 
on  their  outer  surface  more  fibrous 
bark.  As  the  season  advances, 
the  activity  of  these'  cells  becomes 
less  and  less,  and  finally  growth 
ceases  during  the  winter.1 

Stems  of  plants  like  the  corn,  bam- 
boo, and  palm  have  no  true  cambium 
layer,  and  therefore  even  in  the  case 
of  plants  of  this  type  that  live  on 
from  year  to  year  no  annual  rings  are 
formed.  In  the  growth  of  these  stems, 
new  bundles  develop  in  the  pith  be- 
tween those  already  formed. 


III.     THE  STRUCTURE  AND  ADAPTATIONS  OF  LEAVES 

65.  Leaf  arrangement.2  —  Along  the   sides  of  twigs  leaves  are 
arranged  in  such  a  way  as  to  secure  as  much  light  as  possible  with- 
out being  shaded  by  the  leaves  above  them.     Thus  in  plants  like 
the  horse-chestnut,  maple,  and  lilac,  the  leaves  are  arranged  so  that 
at  a  given  level  on  the  twig  two  leaves  are  opposite  each  other, 
while  the  next  pair  are  at  right  angles  to  the  first  pair.     This  is 
known  as  an  opposite  arrangement.     The  beech,  elm,  and  rose,  on 
the  other  hand,  have  an  alternate  arrangement,  only  one  leaf  being 
found  at  a  given  level  on  the  twig. 

66.  External  structure  of  a  horse-chestnut   twig.  —  Laboratory 
Study  No.  34.  —  (Optional.)     (Maple,  beech,  or  other  woody  twig 
may  be  used  with  slight  verbal  changes.) 

1  Sometimes  trees  form  more  than  one  ring  during  a  season. 

2  Before  assigning  this  sect'ion  for  study,  the  teacher  should  dem- 
onstrate from  leafy  twigs  (e.g.   maple,  horse-chestnut,  lilac,  elm, 
apple)    the    characteristic   differences   between   the   opposite   and 
alternate  arrangement  of  leaves. 


THE  NUTRITIVE   ORGANS   OF  PLANTS 


53 


A.  Leaf  scars.     (The  horseshoe-shaped  scars  with  the  raised  dots 

like  horseshoe  nails  indicate  the  places  where  the  stalks 
of  the  leaves  were  attached.) 

1.  Do  the  leaf  scars  occur  in  pairs,  or  is  there  only  one  scar 

at  a  given  level?    How,  therefore,    were   the  leaves   ar- 
ranged on  the 
stem? 

2.  Count  the  num- 

ber of  dots  on 
several  differ- 
ent leaf scars ; 
these  dots  are 
the  ends  of 
the  wood 
bundles  that 
carried  sap  to 
the  various 
leaflets.  Look 
at  the  picture 
ofhorse-chest- 
nut  leaves. 
(See  Fig.  20, 
K.)  How 
many  main 
veins  do  you 
find  in  one 
compound 
leaf?  Com- 
pare this 

number  with  the  number  of  dots  on  the  leaf  scars ;  what 
do  you  conclude  ? 

B.  Buds.     (At  the  end  of  most  twigs  is  a  single  terminal    bud; 

the   buds   along  the   side   of   the  twig  are   lateral   buds. 
Each  bud  is  covered  with  bud-scales.) 

1.  State  the  position  of  each  kind  of  bud  on  the  twig.    Where 
are  the  lateral  buds  found  with  reference  to  the  leaf  scars  ? 


FIG.  19.  —  Spray  of  young  apple  tree,  showing 
alternate  arrangement.  At  the  base  of  each 
leaf  stalk  is  a  pair  of  small  stipules.  —  (Bailey.) 


FIG.  20.  —  Forms  of  leaves.  —  (Courtesy  of  Furman  and  Miller,  Botanical  Aid, 
Western  Publishing  Co.,  Chicago,  111.) 

Simple 


A,  lilac  ;                      C,  white  oak  ;               G,  oak  ; 

7,  sweet  gum  ; 

B,  chestnut  ;               D,  celandine  ;               H,  geranium  ;               J,  buttercup  ; 

Compound  leaves 

E,  locust  ; 

L,  cinquefoil  ; 

F,  wild  tamarind 

K,  horse-chestnut  ; 

M  ,  wild  strawberry  ; 

(twice  compound). 

54 

THE  NUTRITIVE  ORGANS  OF  PLANTS  55 

2.  Look  carefully  at  the  scales  of  the  terminal  bud  to  see  if  they 

have  any  definite  arrangement.  State  whether  or  not  this 
arrangement  corresponds  to  that  of  the  leaf  scars. 

3.  (Demonstration.)     Examine  a  terminal  bud  from  which  one 

or  two  scales  have  been  removed.  Bud-scales  are  modified 
leaves.  How  do  these  scales  differ  from  ordinary  leaves  ? 
What  is  the  use  of  the  scales  to  the  bud  ?  How  are  they 
adapted  for  this  use  ? 

C.  Bud-scale  scars.     (These  are  also  called  annual  scars  because 

they  are  formed  at  the  beginning  of  the  growing  season  of 
each  year  when  the  terminal  bud  opens  and  its  scales  fall 
off.     To  prove  this,  remove  one  or  two  outside  scales  from 
a  terminal  bud,  and  note  the  scar  thus  formed.) 
1.  How  many  groups  of  bud-scale  scars  or  annual  scars  do  you 

find  on  the  twig  you  are  studying  ? 

•  2.  Since   one  set  is  formed  each  spring,  how  many  years  of 
growth  are  shown  on  the  twig  ? 

D.  Breathing  pores  or  lenticels.     Look  for  small  elevations  on  the 

bark.     These  locate  the  lenticels.     Describe  the  lenticels. 

E.  Make  a  careful  outline  drawing  of  the  twig,  showing  its  form, 

the  position  and  shape  of  the  leaf  scars  with  their  woody 
bundles,  the  terminal  and  lateral  buds,  bud-scales,  bud- 
scale  scars,  and  lenticels.  Label  each  of  the  structures 
shown  in  your  drawing. 

67.    The  structure  of  leaves.  —  Laboratory  Study  No.  35. 
A.    Parts  of  a  leaf. 

1.  Examine  a  simple  leaf,  e.g.  maple,  geranium,  or  lilac, 
and  note  that  it  is  made  up  of  the  following 
parts :  a  leaf-stalk,  which  attaches  the  main  part 
of  the  leaf  to  the  stem  of  the  plant,  and  the 
blade,  the  flat,  expanded  portion. 

a.  How  does  the  blade  differ  in  form  from  the  leaf- 

stalk? 

b.  Hold  the  leaf  to  the  light.     How  many  main  veins 

do  you  find?    Where  are  they  smallest?     By 
what  are  the  main  veins  connected  ? 


56  PLANT  BIOLOGY 

c.  Make  a  drawing,  natural  size,  by  tracing  the  out- 
line of  the  leaf-stalk  and  blade.  Draw  carefully 
the  principal  veins  and  a  few  of  their  branches, 
being  careful  to  show  their  relative  size  and  their 
connections.  Label  leaf -stalk,  blade,  main  veins, 
network  of  veins. 

2.  (Optional.)  Examine  a  compound  leaf,  e.g.  rose,  clover, 
locust,  pea,  horse-chestnut.  Notice  that  the  blade  is 
divided  into  three  or  more  parts  known  as  leaflets, 
which  are  attached  either  to  the  end  of  the  leaf- 
stalk or  on  either  side  of  the  mid-vein  of  the  com- 
pound leaf. 

a.  In  what  respect,  therefore,  does  the  blade  of  a  com- 
pound leaf  differ  from  the  blade  of  a  simple  leaf? 

6.  Compare  the  arrangement  of  the  leaflets  in  a  leaf  like 
the  rose,  locust,  or  pea  with  that  in  the  Virginia 
creeper  or  horse-chestnut.  Which  leaves  have  the 
leaflets  arranged  like  the  bones  in  the  palm  of  the 
hand  (palmately  compound),  and  which  have  the 
leaflets  arranged  along  the  side  of  the  mid-vein  as  in 
a  feather  (pinnately  compound,  from  Latin,  pinna  — 
feather)  ? 

c.  At  the  base  of  the  leaf-stalk  of  the  rose,  clover,  or  pea  leaf, 
notice  two  leaf-like  objects  (small  in  the  case  of  the 
rose).  These  are  known  as  stipules.  Stipules  are  also 
found  as  a  part  of  many  simple  leaves.  How  do 
stipules  differ  from  the  other  parts  of  leaves  ?  (See 
Fig.  19.) 

B*  Gross  structure  of  leaves.  —  Secure  thick  leaves  such  as 
sedum,  tulip,  hyacinth,  or  onion. 

1.  Peel  off  from  the  upper  and  lower  surface  a  thin 
membrane  known  as  the  epidermis.  Hold  the 
epidermis  between  yourself  and  the  light.  Tell 
what  you  have  done  and  state  two  characteristics 
of  epidermis. 


THE  NUTRITIVE  ORGANS  OF  PLANTS  57 

2.  Examine  the  material  left  after  removing  the  epi- 

dermis, scraping  it  with  a  knife.  This  inner 
region  of  the  leaf  is  known  as  mesophyll  (Greek, 
meso  =  middle  +  phullon  =  leaf).  Describe  the 
mesophyll,  stating  how  it  differs  from  the  epi- 
dermis. 

3.  Look  carefully  for  veins  in  the  mesophyll.     Describe 

their  appearance. 

4.  (Optional.)     Make  a  diagram  at  least  half  an  inch  in  thick- 

ness of  a  small  portion  of  the  cross  section  of  the  leaf 
you  are  studying,  labeling  upper  epidermis,  mesophyll, 
veins,  and  lower  epidermis. 

C.   Microscopical  structure  of  leaves.  —  Demonstration. 

1.  Strip  off  a  piece  of  epidermis  from  one  of  the  thick 
leaves  named  in  B  above ;  lay  it  on  a  glass  slide, 
add  a  drop  of  water,  and  cover  with  a  cover  glass. 
Examine  with  the  low  power  of  the  compound 
microscope,  comparing  the  specimen  with  Fig. 
21.  Notice  the  shape  of  the  cells  of  which  the 


guard-cells  sur- 
rounding a, 
stoma 


/    cells  of  epider- 
mis 


FIG.  21.  —  Lower  epidermis  of  a  leaf.  —  (Strasburger.) 

epidermis  (shown  by  the  faint  outlines  of  their 
walls)  is  composed.  Find  little  oval  bodies  scat- 
tered among  the  cells  of  the  epidermis,  each  hav- 


58 


PLANT  BIOLOGY 


ing  an  opening  in  the  middle.  This  opening  is 
called  a  stoma,  plural  stomata  (Greek,  stoma  = 
mouth).  Each  stoma  is  surrounded  by  two 
guard-cells. 

Make  a  diagram,  greatly  enlarged,  of  a  stoma  with  its 
guard-cells,  together  with  the  cells  of  the  epi- 
dermis that  immediately  surround  it.  Label 
cells  of  the  epidermis,  guard-cells,  stoma. 


upper  epidermis 


chlorophyll  bodies  v   ~ 


air  space 


mesophyll  cells  con- 
taining chloro- 
phyll bodies 


lower  epidermis 


stoma  with  a  guard-cell  on  either  side 
FIG.  22. —  Cross  section  of  a  leaf.  —  (Strasburger.) 

2.  Study  Fig.  22  and  make  out  the  shape  and  location  of 
each  of  the  following  parts  of  which  it  is  com- 
posed :  upper  epidermis,  mesophyll  cells,  chloro- 
phyll bodies,  air  spaces  between  the  cells,  lower 
epidermis,  stoma.  In  your  note -book  make  a 
drawing  considerably  enlarged  showing  a  small 
portion  of  the  cross  section,  and  label  each  part. 

68.    Experiment  to  demonstrate  the  path  of  sap   through 
leaves.  —  Laboratory  Study  No.  36. 

Place  in  red  ink  the  lower  end  of  a  leafy  branch  of  any 
vigorous  plant,  e.g.  geranium  or  bean   seedling,   and  allow 


THE  NUTRITIVE  ORGANS   OF  PLANTS 


59 


it  to  stand  in  sunlight  or  a  warm  place  until  the  red  color 
appears  in  the  leaves. 

1.  Give  an  account  of  the  experiment,  stating  your  observa- 

tions. 

2.  What  do  you  conclude  as  to  the  part  of  the  leaf  through 

which  soil -water  is  distributed  to  different  parts  of  the 
blade? 

3.  What  cells  of  the  root  did  you  find  specially  adapted  for 

absorbing  water  from  the  soil  ?     Through  what  regions 
of  the  root  and  stem  is  sap  carried  up  to  the  leaves? 

69.    Is  water  vapor  given  off  by  the  leaves  of  a  green  plant? 
—  Laboratory  Study  No.  37.     Demonstration. 

1.  Wrap  sheet  rubber  or  thin  oilcloth  about  a  pot  containing 
a  vigorous  plant  which  has  been  thoroughly  watered. 
Tie  the  rubber  or  oilcloth  tightly  about  the  stem  to 
prevent  the  escape  of 
water  from  the  soil.  If 
rubber  tissue  cannot  be 
obtained,  melted  paraffin 
may  be  poured  over  the 
soil,  and  the  pot  painted 
with  hot  paraffin.  Cover 
the  plant  thus  prepared 
with  a  large  bell  jar  with 
the  inner  surface  dry,  and 
stand  it  in  the  sun  for  a 
few  hours. 

a.  Describe  the  preparation  of 

the  experiment,  stating 
the  reason  for  using  the 
rubber  or  paraffin. 

b.  State  your  observations  and 

conclusion. 

c.  Why  is  the  bell  jar  necessary? 

d.  What  becomes  of  the  water 

Vapor    given    off    by    the    FIG.  23.  — Apparatus  to  show  the 
leaves  of  trees?  excretion  of  water  from  a  plant. 


60  PLANT  BIOLOGY 

2.  (Optional.)  Put  the  plant  prepared  as  above  on  one  of  the 
scale  pans  of  a  balance  and  with  it  a  stoppered  graduate 
or  a  stoppered  bottle.  On  the  other  pan  put  weights 
enough  to  equalize  the  balance.  At  the  end  of  24 
hours  put  enough  water  into  the  graduate  or  bottle  to 
cause  the  weights  on  the  two  pans  to  be  equal. 

a.  Describe  the  preparation  of  the  experiment. 

b.  What  volume  of  water  was  necessary  to  equalize  the  weights 

(i.e.  how  much  water  was  given  off  from  the  plant  in 
24  hours)  ? 

c.  In  a  similar  way  add  water  each  24  hours  for  a  week  or 

until  the  plant  shows  signs  of  wilting.  What  is  the  total 
amount  of  water  given  off  during  the  experiment  ? 

d.  Bearing  in  mind  the  relative  amount  of  leaf  surface   of  this 

plant  and  on  the  trees  of  a  forest  of  even  a  few  acres, 
what  would  you  infer  as  to  the  quantity  of  water  given 
off  by  the  trees  of  a  forest  during  a  summer  season  ? 

70.  Leaves  as  organs  for  food  manufacture.  —  While 
studying  the  manufacture  by  plants  of  carbohydrates  (sugar 
and  starch)  we  showed  that  the  raw  materials  necessary  for 
this  process  are  water  and  carbon  dioxid.  We  have  proved 
that  water  enters  the  root-hairs  by  osmosis  and  travels  in  a 
system  of  ducts  through  the  woody  portion  of  roots  and  stems 
out  to  the  leaves.  Here  the  ducts  of  the  stems  connect  with  a 
network  of  veins  containing  similar  ducts  by  means  of  which 
the  soil-water  is  supplied  to  the  cells  that  are  to  manufacture 
the  food.  The  carbon  dioxid  that  is  needed  is  secured  from 
the  air.  This  gas  passes  through  the  openings  (stomata) 
in  the  epidermis,  and  enters  the  air  spaces  in  the  mesophyll, 
and  finally  reaches  the  cells  containing  the  chlorophyll 
bodies. 

The  sunlight  acting  upon  the  chlorophyll  bodies  enables 
them  to  combine  the  elements  found  in  the  water  and  carbon 
dioxid  to  form  carbohydrates.  These,  as  we  have  seen,  are 


THE  NUTRITIVE  ORGANS  OF  PLANTS  61 

probably  used  in  the  manufacture  of  proteins.  In  the  leaves, 
as  elsewhere  in  the  plant,  the  various  foods  are  digested  and 
thus  are  prepared  to  be  carried  by  the  tubular  cells  (sieve 
tubes)  in  the  veins  and  down  through  similar  tubular  cells  in 
the  fibrous  bark.  (Fig.  16.) 

71.  Excretion  of  the  by-products  of  food  manufacture.  — 
We  showed  in  35  that  during  the  process  of  carbohydrate 
manufacture  oxygen  is  set  free,  and  this  gas  is  given  off 
through  the  stomata  into  the  air.     Water,  too,  is  a  by-prod- 
uct of  food  manufacture  and  assimilation.     In  the  manu- 
facture of  proteins  mineral  matters  are  necessary,  and  these 
are  carried  up  the  stem  dissolved  in  the  soil-water.     Since, 
however,  the  soil-water  is  such  a  dilute  solution,  great  quan- 
tities of  this  liquid  must  be  supplied ;  hence,  much  more  water 
is  taken  in  than  is  needed  for  food  manufacture  or  making  of 
protoplasm.     This  excess  of  water  is  given  off  in  large  quan- 
tity by  the  leaves  of  green  plants  (see  69). 

The  amount  of  water  thus  excreted  by  leaves  is  regulated 
more  or  less  by  the  action  of  the  guard-cells  that  surround  each 
stoma.  When  the  plant  is  well  supplied  with  water,  the  stoma 
remains  wide  open.  If,  on  the  other  hand,  the  leaves  lack  a 
sufficiency  of  water,  these  guard-cells  close  in  upon  the  stoma, 
and  so  prevent  undue  loss  of  moisture.  In  plants  having 
leaves  in  a  horizontal  position,  the  stomata  are  mostly  located 
on  the  lower  surface,  the  upper  surface,  which  is  more  exposed 
to  the  sunlight,  being  covered  with  a  continuous  layer  of 
epidermal  cells.  Were  the  epidermis  altogether  absent  from 
leaves,  the  mesophyll  cells  would  soon  lose  so  much  water 
that  they  would  die. 

72.  Storage    of   foods   in   plants.  —  The  foods    that   are 
manufactured  in  the  chlorophyll-bearing  cells  may  be  carr 
ried,  as  we  have  seen,  to  other  parts  of  the  plant,  there  to  be 


62 


PLANT  BIOLOGY 


stored  until  needed.  Whenever  large  amounts  of  starch, 
sugar,  protein,  or  fat  are  thus  stored,  the  organs  containing 
these  substances  frequently  become  enlarged  (e.g.  carrot  (Fig. 
81),  potato  (Figs.  49,  60),  and  onion)  and  the  walls  of  the  cells 
in  these  organs  usually  remain  thin  and  soft,  permitting  the 
inward  and  outward  passage  of  food.  (See  Fig.  9.) 

73.    Summary  of  functions  of  the  parts  of  the  nutritive 
organs  of  green  plants. 


NAME  OP  PART 

WHERE  PART  is  FOUND 

PRINCIPAL  FUNCTION  OR  FUNCTIONS 
OF  PARTS 

Epidermis 

Covering  of  root 

Absorbs    soil-water,    largely 

through  root-hairs 

Epidermis 

Covering  of  stem 

Protects    inner  layers,    pre- 

and leaves 

vents     undue    escape    of 

moisture 

Lenticels 

Brown     bark     of 

Permit  entrance  of  0  and  C02 

stem 

and  escape  of  0  and  C02 

Stoinata 

Epidermis           of 

Permit  entrance  of  0  and  C02 

leaves 

and  escape  of  O  and  CO2 

Guard-cells 

Surround  stomata 

Regulate  escape  of  H20 

Air  spaces 

Between       meso- 

Serve  as  reservoirs  of  0  and 

phyll  cells 

C02  and  water  vapor 

Chlorophyll- 

Mesophyll           of 

Manufacture  carbohydrates 

bearing  cells 

leaves,        green 

bark  of  stem 

Ducts 

Central  cylinder  of 

Transport  soil-water  upward 

root,  woody  part 

through  the  plant 

of  stem,  veins  of 

leaves 

Sieve  tubes 

Fibrous    bark    of 

Transport      digested     foods 

stem,    veins    of 

downward  through  plants 

leaves 

.  "  » 

THE  NUTRITIVE  ORGANS   OF  PLANTS 


63 


NAME  OF  PART 

WHERE  PART  is  FOUND 

PRINCIPAL  FUNCTION  OR  FUNCTIONS 
OP  PARTS 

Wood  cells 

Central  cylinder  of 
root,  woody  part 
of  stem,  veins  of 
leaves 

Resist  forces  tending  to  break 
roots,  stems,  or  leaves 

Cambium  layer 

Between  bark  and 
wood  of  stem 

Provides  for  growth  of  wood 
and  fibrous  bark  or  bast 

Pith 

Interior  of  stem 

Stores  food 

Pith-rays 

Woody  layer  of 
stem 

Transfer   food    across   stem, 
and  store  food 

CHAPTER  VI 

RESPIRATION   AND   THE   PRODUCTION   OF   ENERGY   IN 
PLANTS 

I.   THE  STORAGE  AND   LIBERATION   OF   ENERGY 

74.  Examples  of  energy  in  plants.  —  By  energy  we  mean 
the  capacity  to  do  work.     In  the  preceding  chapters  we 
have  considered  to  some  extent  the  structure  of  various  parts 
of  plants  and  some  of  the  functions  which  they  are  fitted  to 
perform.     Now  to  carry  on  most  of  these  functions  requires 
the  expenditure  of  energy  on  the  part  of  the  plant.     Thus, 
for  example,  roots  in  growing  expend  considerable  energy, 
pushing  their  way  through  the  soil.     Stems  in  like  manner 
exert  energy  in  lifting  to  the  light  and  air  their  weight  of 
branches   and   leaves.     We   know,  too,    that    soil-water   is 
carried  up  through  plants  to  considerable  heights  (several 
hundred  feet  in  very  large  trees),  that  substances  obtained 
from  the  soil  and  air  are  digested  and  transported  from  one 
part  of  a  plant  to  another.     Still  another  form  of  energy 
exhibited  to  a  certain  degree  by  plants  is  heat,  as  the  follow- 
ing experiment  will  show. 

75.  To  prove  that  heat  energy  is  developed  in  growing  seed- 
lings. —  Laboratory  Study  No.  38. 

Secure  two  wide-mouthed  bottles  of  the  same  size  (light- 
ning fruit  jars  will  answer)  and  put  some  wet  blotting  paper 
in  the  bottom  of  each.  Fill  one  of  the  jars  half  full  of  sprout- 
ing peas.  Fill  the  other  jar  half  full  of  peas  that  have  been 
killed  by  being  soaked  in  a  5  per  cent  solution  of  formalin  for 

64 


THE  PRODUCTION  OF  ENERGY  IN  PLANTS          65 

twenty-four  hours.  Rinse  the  seeds  with  boiled  water  to 
remove  the  preserving  fluid.  Get  two  thermometers  that 
have  approximately  the  same  temperature  reading  in  the  air 
of  the  laboratory.1  Push  the  lower  end  of  the  thermometer 
down  among  the  sprouting  seeds  so  that  the  mercury  will  be 
covered  by  the  seeds.  Do  the  same  with  the  second  ther- 
mometer in  the  jar  of  dead  seeds.  Set  the  jars  side  by  side 
in  a  warm  place  for  twenty-four  hours  or  more. 

1.  Describe  the  preparation  of  this  experiment.     In  what 

respects  are  the  conditions  the  same  in  both  jars?  In 
what  one  respect  do  the  two  jars  differ? 

2.  Take  the  temperature  readings  of  the  thermometer  in  each 

of  the  two  jars  and  record  results.  What  difference 
do  you  notice  in  the  temperature  of  the  seeds  in  the  two 
jars? 

3.  What  is  your  conclusion  from  the  experiment  as  to  the 

development  of  heat  energy  in  seedlings? 

76.  Energy  and  its  transformations.  —  We  see  from  the 
preceding  discussion  and  experiment  that  plants  exhibit 
considerable  energy  or  ability  to  do  work.  Animals  and 
man,  however,  show  far  more  striking  proofs  of  the  output  of 
energy  in  their  muscular  movements,  for  example,  in  running, 
swimming,  and  flying.  Various  machines,  also,  enable  us  to 
make  use  of  different  forms  of  energy,  and,  as  we  shall  now 
see,  one  kind  of  energy  may  be  readily  transformed  into 
another  by  means  of  these  machines.  Suppose  we  consider 
the  work  that  goes  on  in  an  electric  power  plant.  The  coal 
that  is  shoveled  into  the  fire-box  beneath  the  boilers  by  the 
process  of  oxidation  liberates  heat,  which  is  one  of  the  forms 
of  energy.  The  heat  changes  the  water  into  steam,  which 
expands  and  so  exerts  its  power  to  run  the  engine,  and  thus 
heat  energy  is  transformed  into  the  energy  of  motion.  When 
the  engine  is  connected  with  a  dynamo,  this  energy  of  mo- 

1  If  a  difference  in  the  reading  of  the  two  thermometers  is  evident, 
this  difference  should  be  computed  in  the  later  readings  on  the  ther- 
mometers. 


66  PLANT  BIOLOGY 

tion  is  changed  into  electrical  energy,  and  this  in  turn  may  be 
converted  into  light  or  heat  energy  in  our  houses  or  into  energy 
of  motion,  as,  for  instance,  in  the  running  of  a  trolley  car. 

77.  Source  of   the  energy  developed  in  living  things.  — 
In  all  these  marvelous  transformations  of  energy  that  we  have 
just  enumerated  no  new  energy  is  created  and  none  is  de- 
stroyed.    Whence,    then,    comes   this   abundant   supply   of 
energy?     We  shall  find  the  probable  answer  to  this  question 
in  considering  again  the  processes  carried  on  in  the  leaves  of 
plants.     From  the  sun  comes  the  radiant  energy  that  is  abso- 
lutely essential  for  the  activity  of  the  chlorophyll  bodies,  by 
which  carbohydrates  are  formed.     In  the  formation  of  these 
compounds,  the  sun's  radiant  energy  is  used  and  apparently 
disappears.1     In  reality,  however,  it  has  only  been  stored  in 
the  chemical  compounds  formed  thereby,  since,  as  we  have 
said  above,  energy  cannot  be  destroyed. 

78.  Oxidation  as  a  means  of  liberating  energy.  —  Let  us 
now  refer  once  more  to  the  processes  that  take  place  in  an 
electric  power  plant.     We  have  just  said  that  the  energy  de- 
rived from  the  rays  of  the  sun  is  stored  up  in  the  wood,  coal, 
and  other  fuel.     In  order  to  set  free  from  these  compounds 
the  energy  they  contain,  the  wood  or  coal  must  be  burned,  or 
in  other  words  combined  with  oxygen.     Every  one  knows  that 
when  we  wish  to  secure  a  large  amount  of  heat  from  our  fuel 
we  open  wide  the  drafts  in  order  to  secure  a  plentiful  supply 
of  oxygen.     We  demonstrated  in  our  studies  in  oxidation 
that  whenever  a  substance  is  burned,  heat  energy  is  liberated 

1  The  authors  are  indebted  to  Mr.  Paul  B.  Mann  of  the  Morris 
High  School  Department  of  Biology  for  the  following  demonstration 
of  the  effectiveness  of  the  radiant  energy  of  the  sun.  Place  a 
radiometer  (usually  found  in  the  physics  equipment  of  schools)  in 
direct  sunlight,  and  then  remove  it  from  the  sun's  rays.  Try  also 
the  effect  of  an  electric  light  by  bringing  the  radiometer  near  the 
light  bulb,  and  then  slowly  removing  it  to  a  distance. 


THE  PRODUCTION  OF  ENERGY  IN  PLANTS         67 

and  usually  light  is  seen.  The  energy  set  free  by  the  oxida- 
tion of  fuel  may  be  transformed  at  one  time  into  light,  at 
another  time  into  motion,  or  again  into  heat. 

It  is  probably  true  that  the  liberation  of  energy  in  living 
plants  is  somehow  due  to  the  action  of  oxygen.  The  pro- 
cess, however,  is  doubtless  extremely  complicated,  and  just 
what  takes  place  no  one  knows.  Certainly  oxygen  in  some 
form  is  essential  for  the  life  of  every  plant  and  animal.  That 
this  is  true  of  plants,  the  following  experiment  will  show. 

79.  To  prove  that  seeds  need   air  in  order  to  grow.  — 

Laboratory  Study  No.  39.     Demonstration  or  Home  Work. 

Secure  two  wide-mouthed  bottles  and  place  in  the  bottom 
of  each  a  wet  sponge  or  some  wet  blotting  paper,  and  pour 
enough  water  in  each  bottle  just  to  cover  the  sponge  or  paper. 
Fill  both  bottles  with  pea  seeds  that  have  been  soaked  in 
water  for  twenty-four  hours.  Insert  a  tightly  fitting  cork 
into  the  mouth  of  one  of  the  bottles  to  exclude  the  air.  Leave 
the  other  bottle  open  to  the  air,  and  add  enough  water  from 
day  to  day  to  make  up  for  the  loss  by  evaporation.  Put 
both  bottles  in  a  warm  place. 

1.  Describe  this  experiment,  showing  in  what  respects  the 

conditions  are  the  same  for  both  groups  of  seeds. 

2.  In  what  one  respect  do  the  two  groups  of  seeds  differ? 

3.  At  the  end  of  several  days  examine  both  bottles  of  seeds, 

and  state  your  observation  concerning  the  amount  of 
growth  in  each  bottle. 

4.  State  clearly  your  conclusion  as  to  the  necessity  of  air  for 

growth  of  pea  seedlings. 

80.  Relation  of  oxygen  and  carbon  dioxid  to  oxidation.  — 
We  have  now  demonstrated  that  seedlings  will  not  grow 
without  air.     Biologists  have  proved  conclusively  that  oxygen 
is  the  element  in  the  air  that  is  essential  for  the  work  of  all 
plants,  and  that  without  it  they  die.     Hence,  we  may  con- 
clude, as  in  the  case  of  the  furnace,  that  the  necessary  energy 


68  PLANT  BIOLOGY 

of  a  plant  is  in  some  way  set  free  by  oxygen  acting  upon 
plant  compounds.  When  oxidation  of  compounds  containing 
carbon  takes  place,  we  find  that  carbon  dioxid  is  produced 
(11).  Now  if  processes  like  oxidation  are  carried  on  in  plants, 
we  should  expect  to  find  that  C02  is  formed.  The  following 
experiment  proves  clearly  that  such  is  the  case. 

81.  To  prove  that  carbon  dioxid  is  formed  during  the 
growth  of  young  seedlings.  —  Laboratory  Study  No.  40. 

In  the  bottom  of  two  large  jars,  (fruit  jars  will  answer) 
place  some  wet  blotting  paper.  Fill  one  of  the  jars  half  full  of 
germinating  peas,  and  place  a  small  wide-mouthed  bottle 
full  of  lime  water  on  top  of  the  seeds.  Screw  the  top  of  the 
jar  on  tightly.  In  the  other  jar  place  a  bottle  of  lime  water 
and  cover  as  in  the  previous  jar.  At  the  end  of  twenty-four 
hours  or  more  examine  the  lime  water  in  both  jars. 

1.  Describe  the  preparation  of  the  experiment. 

2.  Compare  the  condition  of  the  lime  water  in  both  jars. 

What  has  caused  the  change  in  the  lime  water  in  both 
jars? 

3.  Air,  as  we  proved,  contains  a  little  carbon  dioxid.     Bearing 

this  fact  in  mind,  account  for  the  difference  in  the  ap- 
pearance of  the  lime  water  in  the  two  jars. 

4.  What  gas,  therefore,  do  you  find  to  be  given  off  during 

the  growth  of  young  seedlings  ? 


II.   RESPIRATION 

82.  Respiration  in  plants.  —  It  should  be  clear  from  our 
study  thus  far  that  all  plants  require  oxygen,  and  that  this 
oxygen  brings  about  in  plants  a  process  resembling  oxidation 
at  least  in  the  releasing  of  heat  and  other  forms  of  energy 
and  in  the  producing  of  carbon  dioxid.  These  various  pro- 
cesses take  place  in  each  living  plant  cell.  Hence,  every 
cell  uses  oxygen  and  must  necessarily  form  carbon  dioxid. 
This  process  which  goes  on  in  every  living  cell  is  respiration. 


THE  PRODUCTION  OF  ENERGY  IN  PLANTS 


69 


In  green  plants  during  the  night,  when  carbon  dioxid  is  not 
being  used  for  starch  manufacture,  this  gas  is  given  off  to  the 
surrounding  air,  which  probably  is  not  true  to  any  great 
extent  during  the  daytime.  The  taking  in  of  oxygen  and  the 
giving  off  of  carbon  dioxid  by  plants  corresponds  to  breath- 
ing in  animals.  This  exchange  of  gases  is  carried  on 
through  the  thin  wails  of  roots,  through  the  lenticels  of 
stems,  and  through  the  stomata  of  leaves.  The  process  of 
breathing  must  not  be  confused  with  that  of  carbohydrate 
manufacture,  and  the  following  outline  will  show  the  funda- 
mental difference  between  the  two. 


CARBOHYDRATE  MANU- 
FACTURE 

RESPIRATION  (INCLUDING 
OXIDATION) 

Where  carried  on 

In   cells   containing 

In  all  living  cells 

chlorophyll 

When  carried  on 

In  sunlight 

Throughout    life    of 

cell 

Substances  taken  from 

C02 

0 

air 

Substance    formed    in 

Carbohydrates 

C02 

plant 

Waste    substance    ex- 

0 

CO2 

creted  to  air 

Advantage  to  plant 

Manufacture  of  food 

Release  of  energy 

CHAPTER  VII 

REPRODUCTION   IN   PLANTS 

I.    THE  STRUCTURE  AND  FUNCTIONS  OF  FLOWERS 

83.  Necessity  of  plant  reproduction.  —  Every  one  knows 
that  plants  like  peas,  beans,  and  corn  live  but  one  year. 
Shrubs  and  trees,  while  they  often  live  for  many  years,  finally 
die.     This  is  true  of  all  plants.     It  is  evident,  therefore,  that 
unless  there  were  some  means  of  producing  new  plants  to 
take  the  place  of  those  now  living,  all  forms  of  plant  life 
would  soon  cease  to  exist.     The  process  by  which  new  plants 
are  formed  is  known  as  reproduction.     In  the  higher  plants 
this  process  is  carried  on  by  flowers,  the  function  of  which  is 
to  produce  seeds  which  will  develop  into  new  plants.     We  are 
now  to  study  the  various  parts  of  flowers  and  to  consider  the 
work  of  each  part  in  this  process  of  reproduction. 

84.  Study  of    tulip  flower  (spring    study).  —  Laboratory 
Study  No.  41. 

Material:  While  the  trillium  is  a  more  satisfactory  flower  for 
beginning  the  study  of  the  process  of  reproduction,  the  danger 
that  the  wild  flowers  will  become  exterminated  seems  to  make  the 
study  of  the  tulip  advisable,  especially  in  large  city  high  schools. 
The  two  flowers,  however,  are  usually  in  season  at  the  same  time, 
and  if  possible  at  least  a  few  of  the  trilliums  should  be  secured  for 
demonstration.  If  this  is  impossible,  the  distinction  between  calyx 
and  corolla  should  be  taught  from  the  apple  blossom  or  other  com- 
mon flower. 

70 


REPRODUCTION  IN  PLANTS  71 

A.  Floral  envelopes.  —  Most  flowers  have  parts  shaped  more 

or  less  like  leaves  which  have  either  green  or 
bright  colors.  These  parts  are  arranged  in  one 
or  more  circles  and  make  up  the  floral  envelopes. 

1.  How  many  parts  are  there  in  the  floral  envelopes  of  a 

tulip?  State  the  color  or  colors  of  these  parts 
in  the  flower  you  are  studying. 

2.  When  there  are  two  circles  to  the  floral  envelopes,  an 

outer  composed  of  green  parts  and  an  inner  made 
up  of  brightly  colored  parts  (as  in  the  trillium  or 
the  apple  blossom),  distinct  names  are  given  to 
the  various  parts.  The  outer  circle  is  called  the 
calyx  and  its  parts  are  known  as  sepals;  the 
inner  circle  is  called  the  corolla  and  each  of  its 
parts  is  called  a  petal. 

a.  State  the  number  and  color  of  the  sepals  in  the 

calyx  of  the  trillium. 

b.  How  many  petals  do  you  find  in  the  corolla? 

Describe  their  color. 

3.  Draw  a  side  view  of  a  tulip  before  it  has  fully  opened. 

Label  flower-stalk  and  floral  envelopes. 

B.  Essential  organs.  —  In  the  central  part  of  the  flower  are 

the  organs  without  which  the  work  of  the  flower 
cannot  be  performed.  For  this  reason  they  are 
called  the  essential  organs. 

1.  The  organs  arranged  in  a  circle  just  within  the  floral 

envelopes  are  known  as  stamens.  State  the 
situation  and  the  number  of  stamens  in  the  tulip. 
What  is  the  number  of  stamens  in  the  trillium  or 
apple  blossom  ? 

2.  Each  stamen  consists  of  a  stalk  called  the  filament 

and  an  enlarged  part  known  as  the  anther. 
Name  and  describe  each  of  the  parts  of  a  stamen. 

3.  Make  a  drawing  twice  its  natural  size  of  one  of  the 

stamens.     Label  filament,  anther. 

4.  Find  a  flower  the  stamens  of  which  have  a  powdery 

substance  known  as  pollen.  Which  part  of  the 
stamen  produces  the  pollen? 

5.  The  organ  at  the  center  of  the  flower  is  called  the 

pistil.     It  consists  of  three  divisions  at  the  top 


72  PLANT  BIOLOGY 

which  together  are  known  as  the  stigma,  and 
the  remainder  of  the  pistil  known  as  the  ovary. 
Describe  the  pistil  of  the  tulip  (and  of  the  tril- 
lium)  as  to  position,  shape,  and  color  of  its  parts. 

6.  Make  a  drawing  twice  its  natural  size  of  the  pistil. 

Label  stigma,  ovary. 

7.  Cut  thin  cross  sections  of  a  well-developed  ovary, 

lay  them  on  a  dark-colored  background,  and 
study  one  or  more  of  them  with  a  magnifier  to 
make  out  the  following  parts :  wall  of  the  ovary, 
small  objects  within  the  ovary  known  as  ovules. 
(These  ovules  develop  into  seeds.)  Describe 
what  you  have  done  and  tell  what  you  have  seen. 

8.  Make  a  drawing  at  least  an  inch  in  diameter  of  a  cross 

section  of  the  ovary,  labeling  ovary  wall  and 
ovules. 

9.  (Optional.)     Make  a  drawing  (corresponding  in  size  to  that 

called  for  in  6  above)  of  a  lengthwise  section  of  the 
ovary  to  show  wall  of  ovary,  ovules.  Label. 

85.  Study  of  the  gladiolus  flower  (autumn  study).  Lab- 
oratory Study  No.  42. 

Note  to  the  teacher.  —  Be  careful  to  remove  each  flower 
close  to  the  central  stalk,  so  that  the  ovary  may  not  be  in- 
jured. 

A.    Parts  of  the  flower. 

1.  Remove  the  two  leaves  at  the  base  of  the  flower,  since 

these  leaf -like  organs  do  not  belong  to  the  flower. 
The  outer  brightly  colored  parts  of  the  flower  are 
called  the  floral  envelopes.  These  colored  parts 
unite  to  form  a  greenish  tube  below. 

a.  Count  and  record  the  number  of  divisions  of  which 
the  floral  envelopes  are  composed. 

6.  State  whether  or  not  these  divisions  are  all  of  the 
same  size. 

2.  The  slender  stalks  with  purple  tips,  inside,  the  floral 

envelopes,  are  called  stamens.  How  many  sta- 
mens do  you  find? 


REPRODUCTION  IN  PLANTS  73 

3.  The  single  white  stalk  with  three  divisions  at  the  top 

is  the  upper  part  of  the  pistil.     The  dark  green 
body  below  the  tubular  part  of  the  floral  en- 
velopes is  the  lower  part  of  the  pistil. 
Is  the  top  of  the  pistil  in  the  flower  you  are  studying 
lower  or  higher  than  the  stamens  ? 

4.  Make  a  drawing,  natural  size,  of  the  side  view  of  the 

flower,  and  label  the  following  parts :  the  divided 
portion  of  the  floral  envelopes,  the  tubular  por- 
tion of  the  floral  envelopes,  the  stamens,  the 
pistil. 

B.  Essential  organs.  —  The  stamens  and  pistils  are  called 
the  essential  organs  of  flowers  because  without 
them  the  work  of  the  flower  cannot  be  performed. 

1.  Carefully  slit  open  the  tubular  part  of  the  floral 

envelopes  down  to  the  lower  part  of  the  pistil. 

Then  remove  the  floral  envelopes,  leaving  the 

entire  pistil  uninjured. 
a.   State  what  you  have  done. 
6.   To  what  are  the  stamens  attached  ? 
c.   The  enlarged  part  at  the  top  of  the  stamen  is 

called  the  anther,  the  stalk-like  part  is  called  the 

filament.     Name  and  describe  the  parts  of  a 

stamen. 

2.  Make  a  drawing,  natural  size,  of  a  portion  of  the  floral 

envelope  to  which  a  stamen  is  attached.  Label 
division  of  floral  envelopes,  anther,  filament. 

3.  Find  a  flower  the  stamens  of  which  have  a  powdery 

substance  known  as  pollen.  Which  part  of  the 
stamen  produces  the  pollen? 

4.  The  pistil  consists  of  an  enlarged  portion  at  the  base 

called  the  ovary,  a  stalk-like  portion  called  the 
style,  and  a  spreading  portion  at  the  top,  each 
part  of  which  is  called  a  stigma.  Name  and 
describe  each  part  of  the  pistil. 

5.  Make  a  drawing,  natural  size,  of  the  pistil  and  label 

ovary,  style,  stigmas. 

6.  Cut  thin  cross  sections  of  a  well-developed  ovary,  lay 

them  on  a  dark-colored  background,  and  study 
one  or  more  of  them  with  a  magnifier  to  make 


74 


PLANT  BIOLOGY 


7. 


out  the  following  parts:  wall  of  ovary,  small 
objects  within  the  ovary  known  as  ovules. 
These  ovules  develop  into  seeds.  Describe  what 
you  have  done  and  tell  what  you  have  seen. 
Make  a  drawing  at  least  an  inch  in  diameter  of  a 
cross  section  of  the  ovary,  labeling  ovary  wall, 
ovules. 


8.  (Optional.)  Make  a  drawing  (corresponding  in  size  to  that 
called  for  in  7  above)  of  a  lengthwise  section  of  the 
ovary  to  show  wall  of  ovary,  ovules.  -  Label. 

86.    Pollination.  —  We  have  learned  in  our  study  of  flowers 
that  pollen  is  produced  in  the  anther  of  the  stamen,  and  ovules 

in  the  ovary  of  the  pistil. 
Before  an  ovule  can  develop 
into  a  seed,  however,  certain 
portions  of  a  pollen  grain 
and  of  an  ovule  must  be 
combined.  Pollen  must, 
therefore,  be  transferred 
from  the  anthers  to  the 

pistils,  and  to  this  process  is 


stigma - 


stamen  — 


petal 


ovary 


given  the  name  pol- 


FIG. 24.  —  Structure  of  a  plum  blossom. 
(Bailey.) 

lination.     We  shall  now  learn  by  experiment  some 
adaptations  of  the  pistil  for  receiving  and  holding  ^ 
the  pollen. 

87.  Experiment  to  show  pollina- 
tion. —  Laboratory  Study  No.  43. 

Rub  a  small  brush  or  the  end  of 
a  toothpick  over  a  stamen  (e.g. 
tulip,  Easter  lily,  or  gladiolus)  which 
has  an  abundance  of  pollen,  and  FIG.  25. -A  pollen  adhering 

.1         i         i    ,i  •          11  ,1  to  stigma :  B,  pollen  of  plum 

then  brush  this  pollen  over  the  sur-      escaping  from  the  anther  of 

face  Of  the  Stigma.        •  a  stamen.  —  (Bailey.) 


REPRODUCTION  IN  PLANTS 


75 


1.  Describe  what  you  have  done. 

2.  Examine  the  surface  of  the  stigma  with  a  magnifier  and 

state  what  causes  the  pollen  to  stick  to  the  stigma. 

88.  Microscopical  Demonstration  of  Pollen  Grains  and  their 
Development.  —  Laboratory  Study  No.  44.  (Optional.)  Prepare 
some  sugar  solution  by  adding  to  ten  teaspoonfuls  of  water  one 
teaspoonful  of  molasses  or  grape  sugar  and  heat  to  boiling  point. 
Put  some  of  this  sugar  solution  in  a  clean  Syracuse  watch 
glass.  When  the  solution  has  cooled^'mix  with  it  some  pollen 
from  the  flower  of  a  tulip,  a  trillium,  a  sweet  pea,  or  nasturtium. 
Several  of  these  glasses  might  well  be  prepared  with  slightly  dif- 
ferent strengths  of  sugar  solution  and  piled  one  above  the  other  to 
keep  out  mold  spores,  x  Leave  the  glasses  until  the  pollen  grains 
have  germinated.  Study  the  preparation  with  the  low  power  of 
the  compound  microscope. 

1.  Find  some  pollen  grains  that  have  not  begun  to  grow  tubes. 
Describe  the  form  of  one  of  the  pollen  grains. 


FIG.  26.  —  Different  kinds  of  pollen  grains,  highly  magnified,  two  of  them 
forming  pollen  tubes.  —  (Duggar.) 


76 


PLANT  BIOLOGY 


2.  Find  several  grains  that  have  formed  tubes.     What  is  the 

color  and  shape  of  the  tubes  ? 

3.  Make  a  drawing  at  least  a  half  inch  in  diameter  of  a  pollen 

grain  before  it  has  sprouted  and  a  drawing  of  another  grain 
that  has  sprouted.     Label  pollen  grain,  pollen  tube. 

89.  Pollination,  germination  of  pollen  grains,  and  fertili- 
zation. —  We  have  now  learned  that  pollen  by  the  process  of 
pollination  is  carried  to  the  stigma  of  the  pistil  and  adheres 
to  the  stigma  by  a  sticky  substance  which  is  easily  seen  on 
the  stigma  of  the  Easter  lily  and  often  by  hairs,  also,  as  is  the 
case  in  the  tulip  and  gladiolus.  It  has  been  proved  that  this 
sticky  substance  contains  sugar  which  together  with  other 
materials  furnishes  food  for  the  growth  of  pollen  tubes  (see 
88).  As  each  tube  forms,  it  makes  its  way  down  through 
the  stigma  and  style  (if  present),  and  finally  reaches  an  ovule 
in  the  ovary.  The  tip  of  the  tube  now  penetrates  an  opening 
called  the  micropyle  (Greek,  mi  cro  =  small  -\-pula  =  gate  way) 

in  the  ovule.  Part  of 
the  living  substance  of 
the  pollen  grain  now 
unites  with  a  part  of 
the  living  substance  of 
the  ovule.  This  union 
is  known  as  fertilization. 
After  fertilization  has 
taken  place  the  ovule 
develops  into  a  seed. 

90.    The  cellular  na- 
ture of  pollen  and  ovules. 

—  (If  flowers  are  studied 

FIG.  27.  — Pollen  grain  of  lily  and  the  de-     •     fi       onf11Trm    U  ;~  ~110- 
velopment  of  the  pollen  tube,  highly  mag- 
nified.—(After  strasburger.)  gested  that  this  Section 


v  sperin 
,  nuclei 


REPRODUCTION  IN  PLANTS  77 

be  omitted  until  after  the  cellular  structure  of  plants  has  been 
considered.)  When  the  pollen  grains  are  first  formed  in  the 
anther,  each  consists  of  a  single  cell.  Later  the  nucleus  of 
this  cell  divides  and  forms  two  nuclei,  one  of  which  is  the 
generative  nucleus.  The  generative  nucleus  then  divides 
and  forms  two  sperm  nuclei.  The  ovule  is  more  complex 
in  its  structure,  being  composed  of  many  cells  of  different 
kinds.  But  here,  as  is  the  case  with  the  pollen  grain,  there  is 
one  important  cell  that  is  essential  in  the  process  of  reproduc- 
tion, and  this  is  known  as  the  egg-cell  (Figs.  27  and  29,  A). 

91.  The  formation  of  an  embryo.  —  When  the  pollen 
grain  germinates  and  forms  the  tube,  the  sperm  nucleus  is 
carried  by  the  tube  down  through  the  stigma  and  style  into 
the  cavity  of  the  ovary,  and  finally  through  the  micropyle  of 
the  ovule,  until  one  of  the  sperm  nuclei  comes  to  lie  beside 
the  nucleus  of  the  egg-cell.  The  two  nuclei  now  unite  in  the 
process  of  fertilization  to  form  a  fertilized  egg-cell.  The 
nucleus  of  this  cell  then  divides  and  later  the  cell-body,  thus 
forming  two  distinct  cells.  Each  of  these  divides  to  form  two 
cells,  and  the  four  cells  thus  produced  give  rise  to  eight,  then 
sixteen,  thirty-two,  and  so  on,  until  a  many-celled  structure 
is  developed  which  is  a  miniature  plant  called  the  embryo. 
This  embryo,  together  with  other  parts  of  the  ovule,  consti- 
tutes the  seed.  Some  of  the  cells  of  the  embryo  will  later 
form  the  roots,  others  the  stem,  and  still  others  the  leaves 
of  the  plant  (Fig.  29,  A-E). 

Hence,  the  new  plant  formed  by  this  method  of  reproduc- 
tion is  clearly  descended  from  two  different  parents,  one 
parent  flower  furnishing  in  its  pistil  the  egg-cell  and  the 
other  in  its  stamen  the  fertilizing  pollen.  We  may,  therefore, 
give  the  following  as  a  general  definition  of  the  process  we 
are  studying:  Fertilization  is  the  union  of  the  nucleus  of 


78  PLANT  BIOLOGY 

^toowwi  o/nu/l/16  qtWWunfiXlnq       £< 


(MxL  sKaoLoC  Vrtkuvr 


— -VVUlA^toui^ 


FIG.  28.  —  Diagram  of  a 
longitudinal  section  of  a 
pistil  showing  germination 
of  pollen  grains. 

a  sperm  cell  with  the 
nucleus  of  an  egg-cell. 
Only  one  pollen  grain  or 
sperm  cell  can  be  used  in 
fertilizing     each     egg-cell, 
Usually,  however,  far  larger 
numbers  of  pollen  grains  be- 
come attached  to  the  stigma 
than  can   be  used   by  the 
ovules  in  the  ovary.    All  the 


pollen  grains  that  germinate 

produce  pollen  tubes  which  FlG.  29.  ^Fertilization  of  an  ovule  and 
may  be  Said  to  begin  a  tne  early  stages  in  the  development  of 
race  down  the  Stigma  and  «n  embryo. -(Diagrammatic.) 

style.  The  tubes  that  first  enter  ovules  are  the  ones  that 
carry  on  the  process  of  fertilization.  Those  that  are  beaten 
in  the  race  are  of  no  further  use  and  therefore  die. 


EEPEODUCTION  IN  PLANTS  79 

92.  Self-pollination    and    cross-pollination.  —  Pollination, 
we  have  said,  is  the  transfer  of  pollen  from  the  anther  to  the 
stigma.     When  the  pollen  is  carried  from  the  anther  of  a 
flower  to  the  stigma  of  the  pistil  of  the  same  flower,  the  pro- 
cess is  known  as  self-pollination.     In  many  of  the  flowers 
that   are  self-pollinated,    the   anthers   are   above   the   stig- 
mas, and  when  the  pollen  is  ripe,  the  anthers  burst  open  and 
allow  the  pollen  grains  to  fall  upon  the  stigma  or  stigmas. 

If  pollen  is  carried  from  the  anther  of  a  flower  to  the  stigma 
of  the  pistil  of  a  flower  of  the  same  kind  but  on  another  plant, 
this  transfer  is  called  cross-pollination.  Cross-pollination  is 
often  accomplished  by  the  help  of  the  wind,  as  in  the  flowers 
of  the  corn,  of  grasses,  and  of  many  trees.  In  these  cases  the 
pollen  is  dry  and  light,  and  the  pistils  are  usually  hairy  or 
feathery  to  catch  and  hold  the  pollen  grains. 

Most  bright-colored  and  sweet-scented  flowers  (like  the 
pansy  and  the  clover)  are  visited  by  bees  or  other  hairy  in- 
sects which  carry  pollen  on  their  mouth  parts,  bodies,  and 
legs  from  one  flower  to  another,  thus  insuring  cross-pollina- 
tion. We  shall  now  study  the  pansy  as  a  type  of  insect  polli- 
nated flowers. 

93.  Adaptations    of    the    pansy   for    cross    pollination.  — 

Laboratory  Study  No.  45. 

A.  Floral  envelopes.  —  When  there  are  two  circles  to  the  floral 
envelopes,  an  outer  composed  of  green  parts 
and  an  inner  made  up  of  brightly  colored  parts 
as  in  the  pansy,  distinct  names  are  given  to  the 
various  parts.  The  outer  circle  is  called  the 
calyx,  and  its  parts  are  known  as  sepals;  the 
inner  circle  is  called  the  corolla,  and  each  of  its 
parts  is  called  a  petal. 

1.  State  the  number  and  color  of  the  sepals. 

2.  How  many  petals  are  there?     Describe  the  color  or 

colors  of  each. 


80  PLANT  BIOLOGY 

3.  Locate  the  pairs  of  petals  that  are  nearly  alike  in  size 

and  shape. 
State  the  position  of  the  odd  petal. 

4.  On  which  of  these  petals  do  you  find  the  most  strik- 

ing spots  or  lines  of  color  ? 

5.  Make  a  drawing  of  the  pansy  in  its  natural  position, 

front  view,  and  natural  size.  Label  top  petals, 
side  petals,  lower  petal,  hairs  on  side  petals, 
color  spots. 

6.  Remove  the  two  upper  petals,  and  the  two  side 

petals.  Now  observe  the  tapering  projection 
on  the  lower  or  odd  petal  extending  upward  and 
backward  between  the  sepals.  This  is  called 
the  spur. 

a.   Tell  what  you  have  done  and  seen. 

6.  Carefully  remove  the  lower  petal  with  the  spur 
attached,  and  make  a  drawing  of  it,  natural 
size.  Label  the  spur  and  color  spot. 

7.  Slit  open  the  spur.     Is  the  spur  hollow  or  solid  ? 

8.  The  spur  contains  a  sweet  liquid  called  nectar  which 

attracts  the  bees  and  other  insects.  If  you  find 
any  nectar,  describe  it  and  tell  how  you  found 
it.  Describe  the  taste  of  the  nectar. 

9.  In  what  two  ways,  therefore,  may  pansies  attract 

bees? 

10.  On  which  petal  would  a  bee  be  most  likely  to  alight 

in  visiting  a  pansy?  What  is  there  on  this 
petal  to  guide  the  bee  toward  the  supply  of 
nectar? 

11.  (Optional.)   What  structures  on  the  side  petals  might  make 

it  difficult  for  the  bee  to  insert  its  mouth  parts  in 
this  region  ? 
B.   Stamens. 

1.  Observe  the    stamens    arranged    around  the  pistil. 

Carefully  separate  them  with  a  needle  or  pin. 
State  the  number  and  situation  of  the  stamens: 

2.  Carefully  bend  two  or  more  stamens  away  from  the 

pistil,  and  with  the  help  of  a  magnifier  look 


REPRODUCTION  IN  PLANTS 


81 


C.   Pistil. 


on  their  inner  surface.  Tell  what  you  have 
done,  and  state  whether  the  openings  in  the 
yellow  anthers  from  which  the  pollen  is  dis- 
charged are  found  on  the  inner  surface  (next 
the  pistil)  or  on  the  outer  surface  of  the  anther. 


1.  Examine  the  pistil  after  the  stamens  have  been  re- 

moved. Carefully  describe  the  three  parts 
(ovary,  style,  and  stigma)  of  which  it  is  com- 
posed. 

2.  Observe  a  tiny  cavity  on  the  tip  of  the  stigma.     The 

inside  of  this  cavity  is  the  real  stigma  or  stig- 
matic  surface.  Describe  the  shape  and  state 
the  situation  of  the  stigmatic  surface. 

D.   Cross-pollination  of  the  pansy  by  bumblebees. 

1.  Hold  a  pansy  in  its  natural  position. 

a.  State  the  situation  of  the  stamens  with  reference 

to  the  odd  petal  (i.e.  are  they  above  or  below 
this  petal?). 

b.  On  what,  therefore,  will  pollen  probably  fall  if  it 

is  shaken  out  of  the  anthers  ? 

2.  To  determine  whether  or  not  what  you  have  just 

stated  is  true,  thrust  a  slender  tooth-pick  under 

the  stigma  and  then  under 

the  stamens  and  into  the 

spur.       Shake   the    flower 

gently  and  then  withdraw 

the  tooth-pick  and  examine 

the   surface  with   a   hand 

magnifier.     Tell  what  you 

have  done  and  state  whether 

or  not  pollen  is  found  on 

the  tooth-pick. 

3.  Examine  a  bumblebee.     On  what 

part    of    the    insect    (i.e. 

mouth-parts,  head,  or  body) 

would  the  pollen  be  most  pm.  30.  — Head  of  a 

likely  to  fall  when  the  bee  bee. 


82 


PLANT  BIOLOGY 


FIG.  31.— Hind 
leg  of  a  worker 
bee. 


thrusts  its  mouth-parts  into  the 
spur  as  you  have  just  done  with 
the  tooth-pick?  How  are  all 
these  parts  adapted  to  hold 
pollen?  (Compare  with  Figs. 
30,  31.) 

4.  Still  holding  the  pansy  in  its  natural 

position,  notice  and  state  the  posi- 
tion of  the  stigma  with  reference 
to  the  odd  petal. 

5.  Now  push  a  tooth-pick  which  has  pollen 

on  it,  a  second  time  into  the  spur. 
State  whether  or  not  the  tooth- 
pick hits  the  stigmatic  cup  before 
you  get  it  under  the  stigma. 

6.  Why,  therefore,  will  a  bee  that  has  just 

been  to  one  pansy  flower  be  almost 
certain  to  deposit  pollen  on  the  stigmatic  cup 
of  the  next  pansy  it  visits  ? 


7.  (Optional  home  work.)  Write  a  paragraph  on  "The  Visit 
of  a  Bee  to  a  Pansy  Blossom/'  giving  a  complete 
account  of  what  the  bee  does  and  how  it  does  it. 

94.  The  advantages  of  cross-pollination  in  the  pansy.  —  Charles 
Darwin,  the  great  English  biologist,  proved  by  a  long  series  of  experi- 
ments that  seeds  produced  as  the  result  of  cross-pollination  develop 
into  far  more  healthy  plants  than  do  the  seeds  which  are  formed 
after  self-pollination.  Among  the  plants  with  which  he  experi- 
mented was  the  pansy  (Viola  tricolor).  He  planted  in  each  of  five 
pots  seeds  that  had  been  produced  by  cross-pollination,  and  an  equal 
number  of  seeds  that  were  the  result  of  self-pollination.  The  results 
of  the  experiments  are  given  in  his  own  words  as  follows:  "The 
average  height  of  the  fourteen  crossed  plants  is  here  5.58  inches, 
and  that  of  the  fourteen  self-fertilized  2.37;  or  as  100  to  42.  In 
four  of  the  five  pots,  a  crossed  plant  flowered  before  any  one  of  the 
self-fertilized ;  as  likewise  occurred  with  the  pair  raised  during  the 
previous  year.  These  plants  without  being  disturbed  were  now 


EEPEODUCTION  IN  PLANTS  83 

turned  out  of  their  pots  and  planted  in  the  open  ground,  so  as  to 
form  five  separate  clumps.  Early  in  the  following  summer  (1869) 
they  flowered  profusely,  and  being  visited  by  humble-bees  set 
many  capsules  which  were  carefully  collected  from  all  the  plants 
on  both  sides.  The  crossed  plants  produced  167  capsules,  and  the 
self-fertilized  only  17 ;  or  as  100  to  10.  So  that  the  crossed  plants 
were  more  than  twice  the  height  of  the  self-fertilized,  generally 
flowered  first,  and  produced  ten  times  as  many  naturally  fertilized 
capsules. 

"By  the  early  part  of  the  summer  of  1870  the  crossed  plants  in 
all  the  five  clumps  had  grown  and  spread  so  much  more  than  the 
self-fertilized,  that  any  comparison  between  them  was  superfluous. 
The  crossed  plants  were  covered  with  a  sheet  of  bloom,  whilst  only 
a  single  self-fertilized  plant,  which  was  much  finer  than  any  of  its 
brethren,  flowered.  The  crossed  and  self-fertilized  plants  had  now 
grown  all  matted  together  on  the  respective  sides  of  the  superficial 
partitions  still  separating  them ;  and  in  the  clump  which  included 
the  finest  self-fertilized  plant,  I  estimated  that  the  surface  covered 
by  the  crossed  plants  was  about  nine  times  as  large  as  that  covered 
by  the  self-fertilized  plants.  .  .  . 

"The  ensuing  winter  was  very  severe,  and  in  the  following  spring 
(1871)  the  plants  were  again  examined.  All  the  self-fertilized 
were  now  dead,  with  the  exception  of  a  single  branch  on  one  plant, 
which  bore  on  its  summit  a  minute  rosette  of  leaves  about  as  large 
as  a  pea.  On  the  other  hand,  all  the  crossed  plants  without  excep- 
tion were  growing  vigorously.  So  that  the  self-fertilized  plants, 
besides  their  inferiority  in  other  respects,  were  more  tender. 

"Another  experiment  was  now  tried  for  the  sake  of  ascertaining 
how  far  the  superiority  of  the  crossed  plants,  or  to  speak  more  cor- 
rectly, the  inferiority  of  the  self-fertilized  plants,  would  be  trans- 
mitted to  their  offspring.  The  one  crossed  and  one  self-fertilized 
plant,  which  were  first  raised,  had  been  turned  out  of  their  pot  and 
planted  in  the  open  ground.  Both  produced  an  abundance  of  very 
fine  capsules,  from  which  fact  we  may  safely  conclude  that  they  had 
been  cross-fertilized  by  insects.  Seeds  from  both,  after  germinating 
on  sand,  were  planted  in  pairs  on  the  opposite  sides  of  three  pots. 


84  PLANT  BIOLOGY 

The  naturally  crossed  seedlings  derived  from  the  crossed  plants 
flowered  in  all  three  pots  before  the  naturally  crossed  seedlings 
derived  from  the  self -fertilized  plants. 

"The  average  height  of  the  six  tallest  plants  derived  from  the 
crossed  plants  is  12.56  inches;  and  that  of  the  six  tallest  plants 
derived  from  the  self-fertilized  plants  is  10.31  inches ;  or  as  100  to 
82.  We  here  see  a  considerable  difference  in  height  between  the 
two  sets,  though  very  far  from  equalling  that  in  the  previous  trials 
between  the  offspring  from  crossed  and  self-fertilized  flowers.  This 
difference  must  be  attributed  to  the  latter  set  of  plants  having  in- 
herited a  weak  constitution  from  their  parents,  the  offspring  of  self- 
fertilized  flowers ;  notwithstanding  that  the  parents  themselves  had 
been  freely  intercrossed  with  other  plants  by  the  aid  of  insects." 
("  Cross  and  Self  Fertilization  in  the  Vegetable  Kingdom.") 

Darwin,  therefore,  proved  conclusively  by  these  careful 
experiments  (1)  that  pansy  blossoms  which  were  cross-polli- 
nated produced  ten  times  as  many  seeds  as  those  that  were 
self -pollinated ;  (2)  that  the  plants  developed  from  these 
seeds,  produced  as  a  result  of  cross-pollination,  were  far  more 
vigorous  and  prolific ;  and  (3)  that  the  descendants  of  the 
plants  produced  by  self-pollination,  even  when  their  flowers 
were  cross-pollinated,  were  not  able  to  develop  seeds  capable 
of  as  vigorous  growth  as  the  descendants  of  plants  produced 
continuously  by  cross-pollination. 

95.  Prevention  of  self-pollination.  —  We  have  found  that 
the  pansy  is  well  adapted  to  bring  about  cross-pollination, 
and  since,  as  Darwin  proved,  cross-pollination  results  in  seeds 
being  formed. which  produce  much  more  vigorous  and  fruit- 
ful plants,  we  should  expect  that  the  pansy  would  have  de- 
veloped some  means  of  preventing  self-pollination ;  and  this, 
as  we  shall  see,  proves  to  be  the  case. 

The  anthers  of  the  pansy,  as  we  saw,  are  joined  about  the 
pistil  so  as  to  form  a  band,  and  the  openings  for  the  escape  of 


EEPRODUCTION  IN  PLANTS  85 

pollen  are  on  their  inner  surfaces,  next  to  the  style  and  ovary. 
When  the  pollen  is  shaken  out  of  the  anthers,  it  first  collects 
in  the  space  between  the  anthers  and  the  pistil.  In  the  natu- 
ral position  of  the  pansy  blossom  it  should  be  remembered 
that  the  pistil  is  directed  downward,  and  the  end  of  the  stigma 
rests  on  the  lower  petal,  with  the  stigmatic  cup  opening  out- 
ward and  away  from  the  anthers.  Between  the  two  anthers, 
on  the  under  side  of  the  pistil,  and  at  the  end  nearest  the 
stigma,  there  is  a  V-shaped  notch  from  which  the  pollen  may 
readily  escape  when  the  flower  is  shaken  by  the  wind  or 
insects.  Since  the  notch  is  immediately  over  the  groove  in  the 
lower  petal,  the  pollen  falls  into  this  groove  and  cannot  un- 
aided get  into  the  stigmatic  cup,  since,  as  before  stated,  this 
cup  opens  away  from  the  direction  in  which  the  pollen  must 
fall.  That  the  pansy  pretty  effectually  prevents  self-polli- 
nation the  following  results  of  some  of  Darwin's  experiments 
along  this  line  show.  Two  vigorous  pansy  plants  were 
selected  for  the  experiment.  One  was  covered  with  a  net  so 
that  the  bumblebees  could  not  get  at  the  flowers,  and  the 
other  was  left  uncovered.  In  the  uncovered  one  105  fine 
capsules  were  formed,  while  on  the  covered  one  only  18  were 
formed,  and  in  these  only  a  few  good  seeds  developed ; 
and  Darwin  states  that  even  the  few  seeds  formed  were  prob- 
ably due  to  the  agency  of  tiny  insects  that  the  net  could  not 
exclude. 

In  many  other  flowers  in  which  both  pistil  and  stamens  are 
present  we  find  other  devices  for  preventing  self-pollination. 
Some  of  these  are  as  follows:  In  apple  and  pear  blossoms 
the  stamens  usually  ripen  at  different  times  from  the  stigmas 
in  the  same  blossom,  so  that  self-pollination  in  such  cases  is 
impossible.  Likewise,  when  stamens  and  pistils  are  in  differ- 
ent flowers,  as  in  the  pumpkin,  corn,  and  willow,  cross-polli- 
nation is  obviously  necessary,  if  seeds  are  to  be  formed. 


86  PLANT  BIOLOGY 

Moreover,  in  case  cross-  and  self-pollination  take  place  in  a 
given  flower,  it  has  been  proved  that  the  pollen  from  another 
flower  will  usually  grow  down  the  pistil  more  rapidly  than  the 
pollen  produced  in  the  same  flower,  and  so  in  such  cases  fer- 
tilization is  more  likely  to  result  from  cross-pollination  than 
from  self-pollination. 

96.  Cross-pollination  by  insects.  —  From  our  study  of  the 
pansy  we  learned  that  insects  are  attracted  by  bright  colors 
and  sweet  odors.  By  many  observations  biologists  have 


FIG.  32.  —  A,  staminate  squash  blossom  ;  B,  pistillate  squash  blossom. 
(Bailey.) 

learned  that  most  flowers  with  these  characteristics  are  vis- 
ited by  insects,  and  that  these  animals  carry  pollen  from 
blossom  to  blossom,  thus  insuring  cross-pollination.  Any 
one  familiar  with  apple,  pear,  or  other  fruit  trees  has  seen 
that  at  time  of  blossoming  these  trees  are  alive  with  buzzing 
bees,  and  fruit  growers  know  that  were  it  not  for  these  insect 
visitors  their  fruit  crops  would  prove  a  failure.  Some 
plants  (the  squash,  for  example)  have  two  kinds  of  flowers, 
one  kind  containing  stamens,  the  other  pistils.  It  is  evident, 
therefore,  from  what  we  have  already  learned  that  pollina- 


REPRODUCTION  IN  PLANTS 


87 


tion,  fertilization,  and  the  development  of  fruit  and  seeds 
could  not  take  place  in  plants  like  these  if  there  were  not 
some  means  of  transferring  pollen  from  the  staminate 
flowers  to  pistillate  flowers.  One  has  only  to  watch  squash 

blossoms  on  a  sunny  day 
to  know  that  bees  visit 
them  in  great  numbers  and 
that  their  hairy  bodies  are 
dusted  with  yellow  pollen 
as  they  fly  from  flower  to 
flower. 


FIG.  33.  —  Corn  stall:  with  "  tassels  "  (stam- 
inate flowers)  at  the  top.  —  (Duggar.) 


FIG.  34.  —  Developing  ear 
of  corn  (pistillate  flowers) . 
—  (Bailey.) 


97.  Cross-pollination  by  wind.  —  There  are  many  plants, 
however,  which  have  flowers  without  conspicuous  color  or 
odor;  among  these  are  the  grasses,  the  corn,  and  many 
common  trees  like  the  oaks,  birches,  and  pines.  At  the  top 
of  the  corn  stalk  in  midsummer  develop  the  "  tassels," 
and  when  these  are  shaken,  they  scatter  great  quantities  of 


88  PLANT  BIOLOGY 

light,  dry  pollen.  On  another  part  of  the  plant  the  ears  of 
corn  develop.  Each  ear  consists  in  part  of  clusters  of  pistillate 
flowers,  and  the  threads  of  silk  represent  the  styles  of  the 
pistils.  Farmers  know  that  a  single  corn  plant,  growing  in  a 
place  apart  from  other  corn  plants,  will  not  form  vigorous 
ears.  To  secure  a  good  crop,  pollen  must  be  carried  from  the 
tassels  of  one  plant  to  the  silk  of  another,  and  this  is  accom- 
plished in  a  garden  or  a  corn  field  by  the  wind.  Much  more 
pollen  must  be  produced,  however,  by  wind-  than  by  insect- 
pollinated  flowers,  since  in  the  former  case  a  great  deal  more 
is  wasted.  Many  wind-pollinated  flowers,  such  as  grasses, 
have  feathery  styles  to  catch  and  hold  the  pollen  brought  by 
the  wind. 

98.    Summary  and  definitions. 

Floral  envelopes  of  a  flower  =  calyx  +  corolla. 

Calyx:   'composed    of    sepals    (often   green   in   color); 

principal  use,  to  inclose  and  help  protect  the 

essential    organs    from    cold,    rain,    or    biting 

insects. 
Corolla:   composed  of  petals  (usually  bright  colored); 

principal  use  to  attract  insects  and  so  secure 

cross-pollination. 

Essential  organs  of  a  flower  =  stamens  +  pistils. 

Stamens:  usually  composed  of  filament  and  anther; 
use,  to  produce  pollen  grains,  each  containing 
a  sperm-cell. 

Pistil:  usually  composed  of  ovary,  style,  and  stigma 
(or  stigmas) ;  use,  to  produce  ovules,  each  con- 
taining an  egg-cell,  and  to  insure  pollination, 
germination  of  pollen  grains,  and  fertilization. 


REPRODUCTION  IN  PLANTS  89 

II.  THE  STRUCTURE  AND  FUNCTIONS  OF  FRUITS 

99.  Relation  of  fruits  to  reproduction.  —  We  have  already 
learned  that  the  use  or  function  of  flowers  is  to  insure  the 
production  of  seeds.     As  is  generally  known,  seeds  are  found 
in  fruits.     We  are  now  to  study  several  types  of  fruits. 

100.  Study  of  the  bean  or  pea  fruit.  —  Laboratory  Study 

No.  46. 

A .  Outside  of  the  fruit. 

Study  if  possible  young  pods,  well-developed  pods,  and 
pods  that  have  dried;  or  charts  may  be  used 
to  show  the  developing  pods. 

1.  Name  and  describe  the  structure  which  attached  the 

pod  to  the  plant. 

2.  The  main  part  of  the  fruit  or  pod  is  the  pistil,  which 

in  the  bean  or  pea  flowers  consisted  of  ovary, 
style,  and  stigma.  Which  of  these  parts  are 
found  in  the  fruit  you  are  studying?  (Fig.  35.) 

3.  Bean  and  pea  blossoms  have  calyx,  corolla,  stamens, 

and  pistil.  What  parts  of  the  flower  are  present 
in  the  fruit?  What  parts  have  disappeared? 

4.  Make  a  drawing,  natural  size,  of  the  fruit  you  are 

studying  in  the  position  in  which  it  hung  on  the 
plant.  Label  fruit-stalk,  calyx  (if  present),  and 
the  parts  of  the  pistil  that  you  find. 

B.  Inside  of  the  fruit. 

Split  the  pod  lengthwise  into  halves. 

1.  Carefully  move  one  of  the  seeds  in  the  pod ;  is  it  free 

from  the  pod,  or  is  it  attached  ? 

2.  (Optional.)     The  region  of  an  ovary  to  which  seeds  are 

attached  is  called  the  placenta  (as  was  also  the  case 
in  the  ovary  of  flowers).  Locate  the  placenta  in  the 
fruit  you  are  studying. 

3.  (Optional.)     State  whether  or  not  you  find  any  undeveloped 

seeds.  Undeveloped  seeds  probably  never  were  fer- 
tilized. 


90 


PLANT  BIOLOGY 


4.  Draw,  natural,  size  in  the  position  in  which  the  pod 
hung  on  the  plant  the  opened  fruit.  Label  wall 
of  ovary,  developing  seeds  (undeveloped  seeds, 
if  present),  seed -stalk. 


MftMMM 


covtUMd-  ououj 

FIG.  35.  —  Development  of  the  pea  fruit  from  the  pea  flower.  —  (Drawn 
from  Jung  Chart.) 

101.    Study  of  the  cucumber,  Tokay  grape,  cranberry,  or 
tomato  fruit.  —  Laboratory  Study  No.  47. 

A.  Outside  of  the  fruit. 

1.  All  of  the  fruits  named  above  are  developed  ovaries. 

Describe  the  shape  and  color  of  the  fruit  you  are 
studying. 

2.  Make  a  drawing,  natural  size  (or  an  inch  in  diameter 

in  case  the  grape  or  cranberry  is  used).     Label 
fruit-stalk  (if  present),  ovary. 

B.  Inside  of  the  fruit. 

Cut  a  cross  section  of  one  of  the  fruits  you  are  studying. 
1.   Carefully  move  one  of  the  seeds  within  the  fruit ;    is 
it  attached  or  is  it  free  ? 


REPRODUCTION  IN  PLANTS  91 

2.  Make  a  drawing,  natural  size  (or  an  inch  in  diameter 

in  case  the  grape  or  cranberry  is  used),  of  one 
half  of  the  fruit,  and  show  method  of  seed 
attachment. 

3.  (Optional.)     Pinch  a  seed  of  one  of  the  fruits  between  your 

thumb  and  forefinger.  Is  it  hard  or  soft  ?  Is  it  dry  or 
slippery?  Of  what  advantage  are  these  character- 
istics? 

102.  Seed  dispersal.  —  It  is  evident  that  stronger  plants 
will  be  developed  from  seeds  if  the  latter  are  carried  some 
distance  from  the  mother  plant,  for  then  they  will  not  be 
shaded  by  the  mother  plant,  and  the  young  plants  will  have 
more  light,  air,  food,  and  moisture,  if  they  are  not  crowded 
together.     We  shall  now  study  some  of  the  devices  by  which 
plants  secure  the  dispersal  of  their  seeds. 

103.  Seed  dispersal  by  wind.  —  Laboratory  Study  No.  48. 
Study  one  or  more  of  the  following  fruits  :  — 

A.    Winged  fruits. 

1.  The  maple  fruit. 

a.  Find  the  fruit  stalk,  the  two  cells  of  the  ovary  each 
containing  a  single  seed,  the  wing  attached  to 
each  cell  of  the  ovary. 

Hold  between  yourself  and  the  light  a  maple  fruit 
in  the  position  in  which  it  hung  on  the  tree,  and 
draw  it  (X  2).  Label  fruit-stalk,  cell  of  ovary, 
containing  one  seed,  wing,  veins  of  wing. 

6.  Hold  one  of  the  fruits  some  distance  above  the  desk 
and  let  it  fall.  Describe  the  movements  of  the 
fruit  in  falling. 

c.  Of  what  use  are  the  wings  if  the  wind  were  blowing 

while  the  fruit  is  falling,  or  after  the  fruit  has 
fallen  to  the  ground  ? 

d.  Is  the  maple  fruit  a  dry  or  a  fleshy  fruit? 

2.  The  linden  fruit. 

a.  Notice  the  wing-like  attachment  on  the  fruit-stalk. 
Do  the  linden  fruits  occur  singly  or  in  clusters? 


92 


PLANT  BIOLOGY 


Is  the  fruit  hard  or  soft  ?     Draw  in  the  position 
on  which  it  hung  on  the  tree  ( X  2)  the  fruit  that 
is    given    you.     Label    main  fruit-stalk,  wing- 
like  attachment,  single  fruit  stalk,  fruit. 
b.  c.  d.      Answer  questions  given  under  1  (above). 
3.   The  elm  fruit  or  ailanthus  fruit. 

a.  Notice  the  fruit  stalk,  the  single-celled  ovary,  the 

wing  about  the  ovary. 

Draw  ( X  2)  one  of  the  above-named  fruits.     Label 
fruit-stalk,  ovary,  wing. 

b.  c.  d.      Answer  questions  given  under  1  above. 

B.    Tufted  fruits  (or  seeds) . 

1.  The  clematis,  dandelion,  thistle,  or  aster  fruit. 

a.  Find  the  tiny  seed-like  ovary,  containing  a  single 

seed,  and  the  tuft  of  hair.     Draw  ( X  2)  one  of 
the  fruits.     Label  ovary,  tufts  of  hair. 

b.  c.  d.     Answer  questions  under  A,  above. 

2.  The  milkweed  fruit  and  seed. 

a.  (Optional.)     Study  Fig.  36.     Describe  the  way  the  pod 

opens  when  it  is  ripe.     Are  the  seeds  many  or  few  ? 
Draw  one  of  the  fruits  (pods)  to  show  the  method  of 

opening.  Label  fruit-stalk, 
ovary,  seeds,  style. 

b.  Examine  one  of  the  seeds 

that  has  been  detached 
from  the  pod.  Draw 
(X2)  one  of  the  seeds 
with  its  tuft  of  hair. 
Label  seed,  tuft  of  hair. 

c.  Drop   one   of    the    tufted 

seeds  out  of  an  open  win- 
dow when  a  breeze  is 
blowing  or  fan  a  seed 
in  the  laboratory.  State 
your  observation.  What 

FIG.    36.  —  Milkweed    pod  is  One  US6   of  the  tuft  of 

opening.  hair  ? 


REPRODUCTION  IN  PLANTS  93 

104.   Seed  dispersal  by  animals.  —  Laboratory  Study  No. 
49.     Study  one  or  more  of  the  following  fruits : 

A.  Burs  and  stickers. 

1.  Cocklebur. 

a.  Hold  one  of  the  fruits  between  yourself  and  the 
light.  Do  the  hooks  all  curve  toward  one  end 
of  the  fruit  or  in  several  directions  ? 
Notice  the  two  larger  projections  at  one  end  of  the 
fruit.  These  are  the  styles.  Draw  (•  X  2)  the 
outside  of  one  of  the  cockleburs,  showing 
the  direction  of  the  hooks.  Label  ovary, 
hooks,  two  styles  (large  prongs  at  one  end  of 
fruit). 

6.  Rub  one  of  the  cockleburs  on  a  rough  surface  of 
your  clothing  and  try  to  remove  it.  By  what 
means  does  it  cling  to  the  cloth?  How  is  a 
cow  or  other  hairy  animal  adapted  to  disperse 
this  fruit? 

2.  Burdock. 

a.  Each  burdock  consists  of  a  large  number  of  indi- 

vidual fruits.  Hold  the  burdock  to  the  light. 
In  what  directions  do  the  hooks  extend  ?  Why 
is  this  an  advantage  in  securing  the  distribu- 
tion of  fruits? 

b.  Answer  questions  under  1  b  above. 

3.  Bidens  (also  called  pitchforks  or  beggar's  ticks). 

a.  Hold  the  fruit  to  the  light  or  examine  it  with  a 

hand   magnifier.     In   what    direction    do    the 
little  barbs  on  the  two  prongs  of  the  ovary 
extend  ?     Why  is  this  an  advantage  ? 
Draw   (  X  2)   one  of    the  bidens  fruits.      Label 
ovary,  prongs,  barbs. 

b.  Answer  questions  in  1  b  above. 

B.  Fleshy  fruits.     Suggested  as  home  work. 

1.  In  what  ways  are  the  seeds  of  apples,  cherries,  and 
of  many  other  fleshy  fruits  protected  while  they 
are  ripening? 


94 


PLANT  BIOLOGY 


2.  Many  fleshy  fruits  are  dispersed  by  birds  and  other 

animals  which  are  seeking  food.     How  are  these 
animals  rewarded  for  doing  this  work? 

3.  How  are  the  seeds  of  ripe  peaches  and  cherries,  for 

example,  protected  from  injury? 

105.  Fruits  and  their  classification.  —  If  one  were  asked 
to  give  examples  of  fruits,  one  would  doubtless  give  such 
forms  as  apples,  cherries,  and  peaches:  But  it  is  doubtful 
if  he  would  think  of  including  among  fruits,  pea  pods,  pump- 
kins, chestnuts,  and  corn.  To 
the  botanist,  however,  these  are 


FIG.  37.  —  Lengthwise  sec- 
tion of  apple  fruit,  showing 
seeds  attached  to  a  central 
placenta.  —  (Bailey.) 


FIG.  38.  —  Cross  section  of  apple 
fruit,  showing  seeds  and  their  cov- 
erings which  constitute  the  core. 


considered  to  be  just  as  truly  fruits  as  the  forms  commonly 
thought  of  as  fruits.  Let  us  see  why  such  diverse  plant 
products  as  those  just  named  are  all  included  under  the  head- 
ing of  fruits.  Technically,  a  fruit  is  a  ripened  ovary  and  its 
contents  with  any  other  part  of  the  plant  that  is  closely  incorpo- 
rated with  it;  and  since  the  forms  named  above  are  all  ripened 
ovaries  containing  one  or  more  seeds,  it  is  evident  that, 
strictly  speaking,  they  must  be  classed  with  the  fruits  as 
much  as  apples  and  cherries. 

Sometimes  the  flower  contains  a  number  of  pistils  which 
form  a  pulpy  mass,  such  as  the  raspberries  and  blackberries 


REPRODUCTION  IN  PLANTS 


95 


(see  Fig.  40) ;  hence  each  of  these  so-called  berries  is  composed 
of  a  number  of  separate  fruits.  Sometimes  the  end  of  the 
stem  which  bears  the  pistils  becomes  pulpy  and  juicy  and  the 
dry  pistils  are  embedded  in 
its  outer  surface,  as  is  the 
case  with  strawberries  (see 
Fig.  42).  In  other  fruits 
the  ovary  may  form  a  hard 
woody  wall,  as  in  the  nuts 
like  the  chestnut  (Fig.  39) 
and  acorn,  or  the  wall  may 
be  like  a  tough  paper,  as  in 
the  pods  of  peas  and  locusts 
(Fig.  43).  In  still  other 
forms  the  whole  ovary  may 
become  fleshy,  as  in  the  true 
berries,  such  as  the  cran- 
berry, grape,  and  tomato. 
Or  we  may  find  a  combina- 
tion of  a  tough  wall  and  a  fleshy  interior,  as  in  the  pumpkin, 
squash,  and  cucumber.  In  cherries,  plums,  and  peaches  the 
ovary  forms  two  kinds  of  material,  the  inner  very  hard  and 

stone-like  and  the  outer  pulpy. 
In  fruits  like  the  corn  grain 
and  the  wheat  kernel  the  ovary 
wall  is  so  closely  united  with 
the  coats  of  the  single  seed  that 
these  grains  are  commonly  con- 
sidered as  seeds. 

The  facts  just  stated  with 
regard  to  different  kinds  of  fruits  suggest  a  simple  form  of 
classification,  based  largely  on  the  characteristics  of  the  ovary 
walls.  Thus,  for  instance,  all  those  fruits,  such  as  bean  pods, 


FIG.  39.  —  Chestnut   fruits  inside  the 
chestnut  bur.  —  (Bailey.) 


FIG.  40.  —Raspberry  fruits. 


PLANT  BIOLOGY 


grains,  and  nuts,  in  which  the  walls  are 
dry  at  maturity,  are  called  dry  fruits. 
Those  in  which  the  walls  are  pulpy 
throughout,  as  in  the  tomato,  are  termed 
fleshy  fruits;  and  those 
which  are  partly  fleshy 
and  partly  stone-like ,  as 

FIG,  41 .  -  Flower  of  the    -    th    ch  d  h 

strawberry.  —  (Bailey.)  J 

are  called  stone  jruits. 
Another  scheme  for  classifying  fruits  is 

based  upon  the  fact  that  some  fruits  break 

open  when  ripe  and  scatter  their  seeds, 
while  others  remain 
closed.  Examples  of 
fruits  of  the  first  kind 
are  the  bean,  milkweed,  and  pansy,  and 
of  those  that  remain  closed  are  cherries, 
apples,  and  grains.  Whether  or  not  a  fruit 
breaks  open  at  maturity  depends  upon 
the  character  of  the  ovary  wall,  and  this 
in  turn  determines,  as  we  shall  now  see, 
the  method  by  which  its  seeds  are  dis- 
persed. 


FIG.   42.  —  Straw- 
berry. —  (Bailey.) 


FIG.    43.  —  Pea    pod. 
(Bailey.) 


106.   Home   work   on   fruits.  —  Laboratory 
Study  No.  50.     (Optional.) 
Classify  the  fruits  with  which  you  are  familiar  in  a  table  like 
the  following : 


NAME 
OF  FRUIT 

DRY 
FROIT 

FLESHY 
FRUIT 

STONE 
FRUIT 

OPEN 

WHEN 

RIPE 

CLOSED 

WHEN 

RIPE 

SEEDS 
DIS- 
PERSED 
BY  WIND 

SEEDS 
Dis- 
PERSEDBY 
ANIMALS 

Cherry 

X 

X 

X 

CHAPTER  VIII 
PLANT   PROPAGATION 

I.    SEEDS  AND  THEIR  DEVELOPMENT  INTO  PLANTS 

107.  Study  of  the  bean  seed  and  the  development  of  the 
bean  seedling.  —  Laboratory  Study  No.  51. 

Materials:  Dry  bean  seeds  and  seeds  that  have  been  soaked  for 
24  hours.  Sprouted  bean  seeds  and  seedlings  grown  as  follows: 
To  secure  early  stages,  put  seeds  that  have  been  soaking  for  24  hours 
between  layers  of  wet  blotting  paper,  or  bury  them  in  moist  sawdust, 
and  allow  them  to  stand  in  a  warm  place  for  two  or  three  days. 
For  older  stages  of  bean  seedlings  plant  soaked  seeds  in  boxes  con- 
taining moist  sawdust,  sand,  or  earth.  If  some  of  these  boxes  are 
put  in  a  warm  place  and  others  in  a  cool  place  all  stages  may  be 
obtained  in  two  to  four  weeks. 

1.  What  difference  do  you  notice  in  the  size  of  the  dry  and 

soaked  seed?  How  do  you  account  for  this  dif- 
ference ? 

(Optional.)  Half  fill  a  bottle  with  dry  bean  seeds,  and  add 
water  enough  to  fill  the  bottle.  Allow  the  seeds  to 
soak  for  24  hours.  How  much  do  beans  increase  in  size 
when  soaked  ? 

2.  On  one  edge  of  a  soaked  seed  find  a  scar  called  the  hilum, 

which  marks  the  place  where  the  bean  was  attached 
to  a  small  stem  which  connected  it  to  the  pod. 
Locate  the  hilum,  and  state  what  caused  this  scar. 

3.  Make  a  sketch  about  two  inches  long  of  the  seed,  show- 

ing the  edge  on  which  the  scar  is  found.     Label 
scar  or  hilum. 
H  97 


PLANT  BIOLOGY 


4.  Pinch  a  soaked  seed,  and  notice  the  opening  near  the 

hilum  through  which  water  is  forced  from  the 
seed.  This  opening  is  called  the  micropyle  (Greek, 
micro  =  tiny  -f-  pula  =  gateway). 

a.  Describe  the  position  and  appearance  of  the  micro- 

pyle.    What  is  the  derivation  of  the  word  ? 

b.  Sketch  the  micropyle  in  your  drawing  in  3  above. 

5.  Carefully  remove    the    seed-coat   from  a  soaked  bean. 

All  the  structures  within  this  seed-coat  together 
form  a  little  bean  plant,  called  a  bean  embryo. 
Break  off  one  of  the  two  halves  and  make  out  the 
following  parts  of  the  bean  embryo:  1)  the  two 
thickened  halves  of  the  bean  called  the  seed  leaves 
or  cotyledons;  2)  a  little  sprout,  the  first  stem  or 
hypocotyl  (Greek,  hypo  =  beneath  +  cotyl  =  cotyle- 
don) ;  and  3)  the  two  tiny  folded  leaves  forming 
the  first  bud  or  plumule,  lying  between  the  cotyle- 
dons. 

a.  State  what  you  have  done  to  show  the  parts  of  the 

embryo. 

b.  Name  and  describe  each  of  these  parts. 

c.  Place  the  cotyledon  you  have  removed  close  to  its 

point  of  attachment  to 
the  hypocotyl,  and 
make  a  drawing  about 
two  inches  long,  show- 
ing all  the  parts  named 
above,  labeling  each 
part. 

6.  Examine  a  bean  seed  that 
has  just  begun  to 
sprout. 

a.  Name    the    part    of    the 

bean  embryo  that  first 
breaks  through  the 
seed -coats. 

b.  Make    a    drawing    about 

two    inches   long,    to 

FIG.  44.  —  Germination  of  castor  show      the      Sprouted 

bean.  —  (Osterhout.)  Seed.      Label. 


PLANT  PROPAGATION 


7.  Look  at  a  pot  of  young  seedlings  that  are  just  pushing 

their  way  above  the  surface  of  the  soil  or  sawdust. 

a.  Which  part  of  the  embryo  first  appears  above  ground  ? 

b.  What  is  the  shape  of  this  part  ? 

8.  Study  a  whole  seedling  at  this  stage  (see  7  above), 

from  which  one  cotyledon  has  been  removed. 

a.  Describe  the  changes  that  have  taken  place  in  each 

part  of  the  embryo  since  the  seed  began  to  sprout. 

b.  Describe  the  position  and  appearance  of  the  main  root 

and  its  branches  that  appear  in  this  stage. 

c.  Make  a  drawing,  natural  size,  of  a  seedling  at  this 

stage  and  show  by  a  horizontal  line  the  ground  level. 
Label  each  part. 

9.  Study  a  well-developed  seedling,  comparing  it  with  the 
stages  already  drawn,  and  answer  the  following 
questions :  ' 

a.  What  changes  in  the  size  of  the  cotyledons  do  you 

notice  as  the  seedling  grows  older?  Most  of  the 
food  for  the  early  development  of  the  seedling  is 
furnished  by  the  cotyledons;  suggest,  therefore, 
the  cause  of  the  change  in  size  of  the  cotyledons, 
which  you  have  noticed. 

b.  What  parts  of  the  developing  embryo  have  changed  in 

color  during  germination ;  how  have  they  changed  ? 


B  c 

FIG.  45.  —  Stages  in  the  development  of  the  squash  seedling.  —  (Bailey.) 


100 


PLANT  BIOLOGY 


c.   What  parts  of  the  oldest  seedling  have  developed  from 

the  plumule? 

10.  Draw  the  oldest  stage  of  the  bean  seedling,  and  label 
main  or  primary  root,  root-branches  or  secondary 
roots,  ground  level,  cotyledons  (or  scar  left  by  coty- 
ledons), hypocotyl,  stem  above  cotyledons  (epicotyl), 
leaves,  terminal  bud. 

108.  Study  of  the  corn  seedling  and  its  development  from 
the  corn  grain.  —  Laboratory  Study  No.  52.  (Optional.) 

Materials:  Dry  and  soaked  corn  grains;  seedlings  of  various 
sizes  grown  as  described  above  for  the  bean  seedling.  Corn  grains 
should  be  planted  with  the  pointed  end  down. 

The  structure  of  the  corn  grain  and  the  development  of  the  com 
embryo  can  be  understood  much  more  easily  if  the  study  of  the 
corn  seedling  is  made  first,  and  later  that  of  the  corn  grain. 

A.   Seedling  just  breaking  ground. 

1.  Examine  a  pot  of  seedlings  that  are  just  pushing  their 

way  through  the  soil  or  sawdust,  and  study  a 
seedling  of  this  stage  that  is 
given  you.  All  the  parts  of 
the  seedling  above  the  corn 
grain  have  developed  from 
the  first  bud  or  plumule. 

a.  What  is  the  shape  of  the  part  that 

first  breaks  through  the  soil? 

b.  Look   for   the   sheath   leaf  sur- 

rounding the  unfolding 
leaves,  and  trace  it  down  to 
the  ridge  around  the  stem 
from  which  it  springs.  How 
does  this  sheath  or  first  leaf 
of  the  plumule  differ  from 
the  unfolding  leaves?  What 
is  its  probable  use? 

2.  Observe  the  scar  on  the  grain,  showing  where  it  was 

fastened  to  the  cob,  and  notice  the  shape  of  the 


FIG.  46.  —  Wheat  Seedling. 


PLANT  PROPAGATION  101 

grain  at  its  opposite  end.  Does  the  plumule 
develop  from  the  blunt  end  or  the  pointed  end  ? 
3.  Make  a  sketch  of  the  seedling  (X  2)  and  label  grain  of 
corn,  scar  where  grain  was  attached  to  the  cob, 
stem  of  plumule,  sheath  leaf,  unfolding  leaf,  main 
root,  rootlets,  soil  line. 

B.  Corn  grain  just  sprouting. 

1.  Examine  a  corn  grain  that  has  just  sprouted.     Recall 

to  mind  the  end  of  the  grain  from  which  the  main 
root  grew.  (If  you  are  not  sure,  look  at  your 
drawing,  or  better  yet  the  seedling.) 

a.  What  part  of  the  little  corn  plant  breaks  through  the 

covering  first? 

b.  What  other  part  of  the  embryo  shows  signs  of  growth? 

2.  Remove  the  thin  covering  from  the  grain,  and  observe 

an  oval  body  embedded  in  the  corn  grain.  This  is 
the  little  corn  plant  or  embryo.  How  does  the 
embryo  differ  in  color  from  the  rest  of  the  grain? 

3.  The  oval-shaped  body  from  which  the  root  and  plumule 

seem  to  spring  in  the  grain  of  corn  is  called  the 
cotyledon.  The  remainder  of  the  grain  is  endo- 
sperm, which  is  the  food  material  for  the  develop- 
ment of  the  embryo.  Make  a  sketch  of  the  seed- 
ling at  this  stage  (X2)  and  label  single  cotyledon, 
plumule,  endosperm  or  food  material,  main  root. 

C.  Corn  grain. 

1.  Very  carefully  scrape  away  a  little  of  the  surface  of  the 

cotyledon  of  a  dry  or  soaked  grain  till  the  other 
parts  of  the  little  plant  or  embryo  come  into  view. 
Make  out  the  plumule  and  main  root. 
Sketch  the  corn  grain  and  label  cotyledon,  plumule, 
tiny  root,  food  material  around  the  plant  (endo- 
sperm). 

2.  Cut  a  corn  grain  in  such  a  way  as  to  divide  the  embryo 

and  endosperm  lengthwise  in  half.  Put  one  half  in 
iodine.  Where  in  the  corn  grain  is  starch  pres- 
ent? Where  is  it  absent? 


10f2  '  P'LANT  BIOLOGY 

D.   Corn  seedling  well  advanced. 

1.  What  changes  have  taken  place  during  the  development 

of  the  seedling  in  the  roots?  in  the  plumule? 

2.  How  does  the  veining  of  the  leaves  in  the  corn  plant 

differ  from  that  in  the  leaves  of  the  bean  plant  ? 

3.  Where  do  you  find  aerial  or  air  roots  on  the  corn  seedling? 

(Roots  growing  above  ground  are  aerial  roots.) 

4.  Pinch  the  grain  between  your  fingers.     What  changes 

do  you  notice  in  the  amount  of  food  material?     How 
can  you  account  for  these  changes  ? 

5.  Make  a  sketch  of  the  seedling  and  label  corn  grain,  coty- 

ledon, stem,  leaves,  aerial  roots,  soil  roots. 

109.     Suggestions  for  growing  seedlings  at  home.      (Optional.) 

A.  Window  box.  —  Secure  a  wooden  box  at  least  six  inches  in 
depth,  and  of  a  convenient  size  to  place  in  front  of  a  south  window, 
if  you  have  such  a  window  at  home.     Nearly  fill  the  box  with  rich 
earth  which  has  been  finely  pulverized  or  sifted.     If  possible,  mix 
in  thoroughly  some  well-rotted  manure  and  a  tablespoonful  of  pre- 
pared fertilizer.     Soak  your  seeds  for  twenty-four  hours,  and  plant 
them  at  a  depth  equal  to  four  times  the  thickness  of  the  seeds. 
Cover  the  seeds  with  dirt,  press  it  down  firmly,  and  sprinkle  with 
water  till  the  earth  is  thoroughly  moistened  to  a  depth  of  at  least 
four  inches.     See  that  your  garden  is  kept  as  nearly  as  possible  at  a 
temperature  of  70  degrees.     Add  enough  water  day  by  day  to  keep 
the  ground  moist. 

B.  Tumbler  garden.  —  Secure   several  pieces  of   blotting  paper 
or  other  porous  paper,  and  cut  it  about  as  wide  as  the  tumbler  is 
high.     Wet  the  paper  and  roll  it  into  a  hollow  cylinder  that  fits 
inside  the  tumbler.     Between  the  blotting  paper  and  the  glass 
place  the  soaked  seeds  with  their  hilums  in  several  different  posi- 
tions.    Fill  the  interior  of  the  tumbler  with  wet  sawdust,  cotton,  or 
crumpled  paper.     Cover  the  tumbler  loosely  and  keep  the  contents 
moist,  and  at  a  temperature  of  about  70  degrees. 

C.  Glass-plate  garden.1  —  Secure  two  pieces  of  glass  about  5X7 

1  The  authors  are  indebted  to  Dr.  Cyrus  A.  King,  Head  of  Depart- 
ment of  Biology  of  Erasmus  Hall  High  School,  Brooklyn,  N.  Y.,  for 
this  method  of  germinating  seeds. 


PLANT  PROPAGATION 


103 


inches  (picture  negatives  cleaned  in  hot  water  are  admirable  for 
this  purpose).  Upon  one  of  the  glasses  put  a  layer  of  wet  cotton 
wadding  about  half  an  inch  thick.  Arrange  the  seeds  (which  have 
been  soaked  for  24  hours)  with  their  hilums  in  several  different 
positions,  and  place  on  top  of  them  the  second  plate  of  glass.  Tie 
strings  about  the  two  glasses,  and  stand  the  "garden"  in  about  an 
inch  of  water.  The  water  will  rise  between  the  glasses  and  keep  the 
developing  seedlings  moist.  After  the  seeds  have  begun  to  sprout, 
turn  the  " garden"  so  that  it  rests  on  another  edge,  and  note  the 
effect  on  direction  of  growth  of  the  hypocotyl. 


Observations  to  be  made  on  the  development  of  each  seed 

1.  What  part  of  the  seedling  first  appears  above  ground  ?     (Make 

drawings.) 

2.  Does  this  part  come  up  straight  or  in  the  form  of  an  arch  ? 

3.  What  kind  of  veining  is  found  in  the  leaves  ? 

4.  How  many  cotyledons  are  present,  and  what  is  their  use  ? 

5.  In  what  direction  does  the  main  root  tend  to  grow  ?  the  sec- 

ondary roots  ? 

110.  Comparison  of  seeds  and  seedlings.  —  Study  No.  53. 
(Optional.) 

Soak  and  plant  at  home  as  directed  under  Materials  (107), 
several  kinds  of  seeds.  Study  the  seeds  and  seedlings,  and  fill  out 
in  your  note-book  a  table  like  the  following : 


BEAN 

PEA 

SQUASH 

CORN,  ETC. 

Number  of  cotyledons  -  . 



Position  of  stored  food  . 

Kinds  of  food  present    .     .     . 



104 


PLANT  BIOLOGY 


Function  of  cotyledons      .     . 

(Storage  of  food)  .... 

f  T*Y»liafipp^ 

Method  of  breaking  ground   . 

(By  arched  hypocotyl)    . 

Veining  of  foliage  leaves    .     . 
(Npttpd^l 

fpQrQiipi\ 

111.     Nutrients  stored  in  corn  grains  for  the  use  of  the  seedling. 
—  Laboratory  Study  No.  54.     (Optional.) 

Grind  with  a  mortar  and  pestle  some  corn  grains  till  a  fine  meal 
is  prepared.  Test  for  each  of  the  food  substances  and  fill  out  in 
your  note-book  a  table  like  the  folbwing : 


NAME  OF  NUTRIENT 

CHEMICAL  USED 

RESULT 

CONCLUSION 

Fat  1 

112.  Of  what  importance  is  the  endosperm  in  the  develop- 
ment of  corn  seedlings  ?  —  Laboratory  Study  No.  55.  Home 
work  or  demonstration. 

Soak  twenty-four  or  more  corn  grains  over  night.  Care- 
fully remove  from  half  of  them  all  the  endosperm  (food 

1  To  test  for  fat,  put  some  of  the  cornmeal  into  a  test  tube,  add 
some  ether,  shake  frequently,  and  let  the  tube  stand  for  a  time.  At 
the  end  of  twenty-four  hours  pour'off  the  clear  liquid  upon  pieces  of 
glazed  paper.  After  the  ether  has  evaporated,  hold  the  paper  to 
the  light.  Be  careful  not  to  hold  the  ether  near  a  flame. 


PLANT  PROPAGATION 


105 


materials)  from  around  the  embryo  corn  plant.  Plant  the 
corn  grains  and  the  corn  embryos  in  rich  soil,  covering  both 
with  the  same  depth  of  earth,  and  marking  the  location  of  the 
two  sets.  Put  them  in  a  warm  place. 

1.  Describe  the  preparation  of  the  experiment. 

2.  At  the  end  of  two  weeks  state  the  number  of  each  group  of 

seedlings  that  have  pushed  through  the  soil. 

3.  What  difference  in  the  size  of  the  two  sets  of  seedlings  do 

you  notice  at  the  end  of  two  weeks?    at  the  end  of 
three  weeks? 

4.  What  has  this  experiment  taught  you  ? 

II.   OTHER  METHODS  OF  PLANT  PROPAGATION 

113.  Grafting.  —  The  method  often  adopted  by  fruit  growers 
to  produce  new  and  better  varieties  is  that  known  as  grafting. 
This  method  of  plant  propa- 
gation may  be  carried  on  in 
the  following  manner.  A 
young  shoot,  known  as  the 
scion  (Fig.  47,  A,  b),  is  cut 


FIG.  47.  —  Methods  of  grafting. 

in  an  oblique  direction  from  a  tree,  the  fruit  of  which  is  desired, 
and  a  similar  oblique  cut  is  made  across  the  twig  of  another  tree, 
called  the  stock  (Fig.  47,  A ,  a) ,  of  a  related  kind.  The  two  freshly  cut 
surfaces  are  then  closely  applied  to  each  other,  and  the  scion  and 


106  PLANT  BIOLOGY 

stock  are  bound  together  by  grafting  wax  (Fig.  47,  B,  c),  which  is  put 
around  the  outer  bark  to  hold  the  two  pieces  in  place  and  to  pre- 
vent evaporation.  In  this  way  the  cambium  layers  of  the  two 
plants  are  brought  into  close  contact  and  soon  unite.  The  ducts  of 
the  stock  likewise  join  those  of  the  scion,  and  so  sap  is  transmitted 
to  the  grafted  twig,  which  grows  and  develops  its  fruit  as  though  it 
were  still  a  part  of  the  plant  from  which  it  was  taken.  There  are 
many  different  ways  of  cutting  and  binding  the  twigs  together, 
and  even  buds  may  be  used  as  scions  (Fig.  47,  C,  6).  But  the  prin- 
ciple is  the  same  in  every  case. 

Grafting  is  of  necessity  employed  in  producing  new  plants  of 
seedless  grapes  or  oranges.  It  is  also  frequently  adopted  to  com- 
bine the  desirable  characteristics  of  two  different  plants.  For 
example,  when  the  vineyards  of  France  were  being  destroyed  by 
an  insect  that  attacked  the  roots,  the  fruit-growers  overcame  the 
difficulty  by  grafting  the  wine-producing  scions  upon  the  more  vigor- 
ous and  resistant  nutritive  stock  of  grapevines  introduced  from 
America. 

114.  Slips,  runners,  and  layers.  — Another  method  of  producing 
new  plants  is  that  of  cutting  twigs  of  plants  that  are  desired,  and 


FIG.  48,  —  Strawberry  plant  with  runner.  —  (Bailey.) 

placing  the  lower  end  of  the  stems  in  moist  sand.  Roots  soon 
develop  on  these  so-called  slips,  and  the  new  plants  thus  formed  can 
then  be  transplanted  into  good  rich  soil.  Any  one  who  has  seen  a 
vigorous  strawberry  plant  knows  that  it  sends  out  a  lot  of  slender 
stems  which  grow  so  rapidly  that  they  are  known  as  runners.  When 
a  portion  of  one  of  these  runners  lies  upon  the  surface  of  moist  soil, 


PLANT  PROPAGATION 


107 


roots  are  formed  as  in  the  case  of  slips,  and  when  they  are  firmly 
established,  the  connection  with  the  parent  plant  may  be  severed, 
and  thus  a  new  strawberry  plant  secured.  Still  another  method 
of  propagating  plants  is  known  as  layering,  which  may  be  accom- 
plished in  raspberry  or  blackberry  plants  by  burying  the  tips  of 
branches  in  the  soil,  thus  inducing  the  production  of  roots.  The 
new  plant  can  then  be  severed  from  the  parent. 

116.   Tubers.  —  New  potato  plants  are  commonly  secured,  not 
by  planting  potato  seeds,  but  by  cutting  into  pieces  a  potato  which 


FIG.  49.  —  Potato  plant   and   tubers  grown  from  dark   colored   potato  in 
center.  —  (U.  S.  Dept.  Agriculture.) 

is  a  fleshy  underground  stem  or  tuber,  each  piece  having  one  or  more 
"eyes,"  and  putting  these  into  the  ground.  In  each  eye  is  a  bud, 
and  when  this  sprouts  it  develops  stems  and  leaves  above  ground, 
the  new  plant  thus  formed  getting  a  considerable  amount  of 
nutrition  from  the  food  stored  in  the  tuber  during  the  preceding 
season. 


108  PLANT  BIOLOGY 

116.  Bulbs.  —  Still  another  method  of   propagating  plants  is 
by  means  of  bulbs,  which,  in  the  onion,  for  example,  consist  of  a  short, 
thickened  underground  stem,  to  which  are  attached  many  layers 
of  thickened  parts  of  leaves  known  as  bulb-scales.     Frequently,  as 
in  the  tulip  and  hyacinth,  after  the  food  stored  in  the  bulb  has  been 
used  in  the  early  spring  to  develop  stem,  leaves,  and  flowers,  the 
nutritive  organs  store  away  food  for  another  season  by  producing 
new  bulbs  close  to  the  old  one. 

117.  Home  bulb  culture.  —  (Optional.) 

Few  plants  are  easier  to  cultivate  or  give  greater  satisfaction, 
especially  in  winter,  than  those  that  grow  from  bulbs.  Secure  a  few 
tulip,  hyacinth,  or  narcissus  bulbs  and  bury  them  in  pots  of  rich 
earth.  Water  them  well  and  put  them  in  a  dark,  cool  place  for  four 
to  six  weeks,  until  the  roots  appear  through  the  opening  at  the  bot- 
tom of  the  pot.  Then  put  them  in  a  warm,  sunny  place,  keep  them 
well  watered,  and  the  flowers  will  appear  in  a  few  weeks. 

III.   CONDITIONS  THAT  ARE  ESSENTIAL  FOR  THE  GROWTH 

OF  PLANTS 

118.  The  five  essential  conditions  for  plant  growth  are  the 
following :    (1)  moisture,  (2)  favorable  temperature,  (3)  air, 
(4)  light,  (5)  food.     We  have  already  shown  the  necessity  of 
air  for  the  germination  of  seeds  (79)  and  for  the  liberation  of 
energy  (76).     The  use  of  the  food  stored  in  the  corn  grain 
for  the  corn  embryo  was  also  demonstrated  in  112.     We  have 
also  proved  that  green  plants  do  not  manufacture  carbohy- 
drates in  the  absence  of  sunlight  (30).     We  can  likewise  show 
experimentally  the  relation  of  moisture  and  temperature  to 
the  germination  of  seeds  and  to  the  growth  of  plants. 

119.  Relation  of  moisture   to   germination  and  growth.  —  Labo- 
ratory Study  No.  56.     (Optional.)     Suggested  as  home  work. 

Secure  three  tumblers  of  same  size  (tin  covered  jelly-tumblers  are 
very  satisfactory).    In  the  bottom  of  each  put  a  piece  of 


PLANT  PROPAGATION  109 

sponge  about  half  the  size  of  the  fist  (a  wad  of  cotton  or  paper 
will  answer).  Label  the  first  tumbler  No.  1,  and  place  upon 
the  sponge  10  pea  seeds  that  have  been  soaked  for  24  hours. 
In  the  second  tumbler  (labeled  No.  2)  put  10  soaked  peas,  and 
add  enough  water  to  come  nearly  to  the  top  of  the  sponge. 
Put  10  soaked  pea  seeds  into  the  other  tumbler  (No.  3),  and 
add  sufficient  water  to  cover  all  the  peas.  To  prevent  the 
evaporation  of  the  water,  cover  the  three  tumblers,  and  place 
them  side  by  side  in  a  moderately  warm  temperature  (65°- 
70°  F.),  and  label  each  "  Please  do  not  disturb." 

1.  Which  one  of  the  five  conditions  (enumerated  in  118  above)  is 

different  for  the  three  groups  of  seeds  ? 

2.  Name  all  of  these  conditions  which  are  practically  the  same  for 

the  seeds  in  all  three  of  the  tumblers. 

3.  At  the  end  of  a  few  days  compare  the  seeds  in  the  three  tum- 

blers. What  percentage  of  the  seeds  in  each  of  the  three  tum- 
blers has  germinated  ? 

4.  State  clearly  your  conclusion  as  to  the  relation  of  water  to  the 

germination  of  pea  seeds. 

5.  Allow  the  three  tumblers  to  stand  side  by  side  in  a  warm,  light 

place  for  several  weeks.  Describe  the  changes  that  take  place 
in  each  tumbler,  and  state  your  conclusion  as  to  the  relation 
of  moisture  to  the  growth  of  pea  plants. 

120.   Relation  of  temperature  to  germination  and  growth.  —  Labo- 
ratory Study  No.  57.     (Optional.)     Suggested  as  home  work. 

Prepare  three  tumblers  with  sponges  (cotton  or  paper)  as  in  119 
above,  putting  in  water  enough  to  come  nearly  to  the  top  of 
the  sponge  in  each  dish.  In  each  tumbler  place  10  soaked 
peas,  and  put  on  the  covers.  Label  No.  1,  No.  2,  and  No.  3. 
Set  tumbler  No.  1  in  the  refrigerator  or  in  some  place  where 
it  will  not  freeze.  Keep  Tumbler  No.  2  at  the  temperature 
of  the  living  room.  Place  No.  3  where  the  temperature  is 
over  100°.  Make  sure  that  all  tumblers  have  about  the 
same  amount  of  light  by  covering  each  with  black  paper  or  a 
cloth.  By  the  aid  of  a  thermometer  find  and  record  the  tern- 


110  PLANT  BIOLOGY 

perature  of  each  place  where  you  put  a  tumbler.  Each  day 
look  at  the  tumblers,  and  if  necessary  add  enough  water  to 
keep  the  level  the  same  in  all  three. 

1.  Which  one  of  the  five  conditions  named  in  118  is  different  for 

the  three  groups  of  seeds  ? 

2.  Name  all  the  conditions  which  are  practically  the  same  for  the 

seeds  in  all  three  of  the  tumblers. 

3.  At  the  end  of  a  few  days  compare  the  seeds  in  the  three  tumblers. 

What  percentage  of  the  seeds  in  each  of  the  three  tumblers 
has  germinated  ? 

4.  State  clearly  your  conclusion  as  to  the  relation  of  temperature  to 

the  germination  of  pea  seeds. 

5.  Allow  the  three  tumblers  to  stand  in  the  three  different  tem- 

peratures for  several  weeks.  Describe  the  changes  that  take 
place  in  each  tumbler,  and  state  your  conclusion  as  to  the 
relation  of  temperature  to  the  growth  of  pea  plants. 

121.  The  soil.  —  "  From  the  soil  all  things  come;  and 
into  it  all  things  at  last  return ;  and  yet  it  is  always  new,  and 
fresh,  and  clean,  and  always  ready  for  new  generations.  This 
soft,  thin  crust  of  the  earth  —  so  infinitesimally  thin  that  it 
cannot  be  shown  in  proper  scale  on  any  globe  or  chart  —  sup- 
ports all  the  countless  myriads  of  men,  and  animals,  and 
plants,  and  has  supported  them  for  countless  cycles,  and  will 
yet  support  for  other  countless  cycles.  In  view  of  this 
achievement,  it  is  not  strange  that  we  do  not  yet  know  the 
soil  and  understand  it ;  and  we  are  in  a  mood  to  be  patient 
with  our  shortcomings."  l 

Even  a  casual  examination  of  the  soil  in  any  region  shows  that 
it  has  a  complex  structure.  Usually  it  is  composed  of  some  coarse 
particles  known  as  gravel,  finer  grains  called  sand,  and  still  more 
minute  ingredients,  the  mud  or  clay.  The  relative  proportions  of 
these  constituents  determine  whether  the  soil  is  a  gravelly  soil,  a 
sandy  soil,  or  a  clayey  soil.  The  soil  particles  to  which  we  have 

1  Bailey's  "  Cyclopedia  of  American  Agriculture,"  Vol.  I,  "  Farms," 
p.  323. 


PLANT  PROPAGATION  111 

referred  supply  the  mineral  ingredients  needed  by  plants  in  the  form 
of  soil-water.  But  soil,  to  be  fertile,  must  contain  a  considerable 
quantity  of  vegetable  mold,  the  so-called  humus,  a  dark  brown  or 
black  substance  produced  by  the  decay  of  vegetable  matter.  This 
is  the  reason  that  florists  mix  with  the  dirt  in  their  flower-pots  a 
handful  of  material  obtained  from  the  floor  of  the  forest  (see 
frontispiece),  where  leaves  have  fallen  and  decomposed  year  after 
year. 

122.  Moisture.  —  If  the  student  has  tried  the  experiment  in 
119,  he  will  have  been  convinced  that  the  amount  of  moisture 
supplied  to  seeds  or  plants  has  a  great  deal  to  do  with  their  develop- 
ment. Soils  in  very  dry  or  arid  regions  are  deficient  in  water, 
and  this  must  be  supplied  by  irrigation.  In  semiarid  regions  proper 
methods  of  tillage,  as  we  shall  see,  will  do  much  to  keep  the  soil 
in  a  proper  condition  for  plant  growth,  so  far  as  moisture  is  con- 
cerned. Very  moist  or  "heavy"  soils,  on  the  other  hand,  are 
unfavorable  for  the  growth  of  most  plants,  and  so  the  excess  of  water 
must  be  removed  by  drainage. 

Reviewing  some  of  the  facts  already  learned,  we  see  that  a  large 
supply  of  water  must  be  secured  by  plants  from  the  soil,  because  — 

"1.  A  living  plant  contains  a  large  proportion  of  water  —  gen- 
erally more  than  75  per  cent  of  its  weight. 

"2.  Large  quantities  of  water  must  pass  through  the  plant  in 
order  that  the  food  solution  in  the  soil  may  be  carried  to  the  leaves, 
and  the  substances  that  it  contains  may  be  converted  into  organic 
matter.  This  water  loss  takes  place  by  transpiration  from  the 
leaves  and  growing  shoots. 

"Careful  and  extended  experiments  in  this  country  and  Europe 
have  shown  that  300  to  500  tons  of  water  are  taken  from  the  soil 
by  the  various  crops  for  each  ton  of  dry  substance  produced."  1 

123.  Relation  of  the  soil  to  air.  —  When  the  interstitial  spaces 
between  the  particles  of  soil  are  not  filled  with  water,  or  when  they 
are  only  partly  filled,  they  contain  air.  The  air  which  circulates  in 

1  Bailey's  "  Cyclopedia  of  American  Agriculture,"  Vol.  I,  "  Farms," 
p.  353. 


112  PLANT  BIOLOGY 

the  soil  differs  in  composition  from  the  air  above  the  surface.  As  a 
rule,  the  soil  air  contains  less  oxygen  and  more  carbonic  acid  (CC>2), 
ammonia,  and  vapor  of  water.  The  increased  amount  of  carbonic 
acid  and  ammonia  have  their  origin  in  the  organic  matter  or  humus. 
A  soil  is  not  in  the  best  condition  for  the  production  of  crops  unless 
there  is  within  its  depths  a  free  circulation  of  air.  This  is  true 
because  oxygen  in  the  soil  is  as  essential  for  the  life  of  the  plant  as 
it  is  for  the  animal.  .  .  . 

"When  the  soil  is  full  of  water  to  within  a  few  inches  of  the  sur- 
face, there  can  be  no  circulation  of  air  among  its  particles.  Ade- 
quate ventilation  can  be  provided  for  such  a  soil  only  by  drainage. 
Drainage  ventilates  the  soil  by  lowering  the  ground  water  three  or 
four  feet,  and  thus  makes  it  possible  for  the  roots  of  plants  to  pene- 
trate soil  more  deeply.  In  time  these  roots  die  and  decay  and 
afford  passageways  throughout  the  soil  for  the  ready  movement 
of  the  air."  1 

124.  Relation  of  soil  to  heat.  —  The  influence  of  the  tempera- 
ture of  the  soil  on  crop  production  is  a  factor  of  considerable 
importance.  The  life  processes  of  a  plant  are  practically  suspended 
below  a  certain  minimum  temperature,  which  is  about  40  degrees 
Fahrenheit  for  most  cultivated  crops.  Above  this  temperature 
all  the  vital  activities,  as  germination  and  growth,  increase  until 
the  optimum  is  reached.  Above  this  point  these  life  processes  de- 
crease in  activity  until  the  point  is  reached  when  they  cease.  The 
soil  is  a  great  factory  that  has  its  production  vastly  increased  as 
the  temperature  rises.  .  .  .  The  minimum  temperature  at  which 
corn  germinates  and  also  the  minimum  for  its  growth  is  48°  or 
49°  F.  Its  optimum  is  about  93°  F.  .  .  . 

"The  sources  of  the  heat  of  the  soil  are  the  internal  heat  of  the 
earth,  the  sun,  and  decaying  vegetable  matter.  It  is  difficult  to 
estimate  to  just  what  extent  the  internal  heat  of  the  earth,  which 
itself  is  very  great,  affects  the  temperature  near  the  surface  of  the 
earth.  However,  the  amount  of  heat  from  this  source  is  insignificant, 
is  a  constant  factor,  and  is  entirely  beyond  the  control  of  man. 

1  Bailey's  "Cyclopedia  of  Agriculture,"  Vol.  IX,  "Farms,"  p.  357. 


PLANT  PROPAGATION  113 

Decaying  organic  matter  furnishes  some  heat  to  the  soil.  For 
example,  manure  heats  the  soil  to  a  limited  extent  when  it  is  spread 
on  the  surface  and  plowed  in.  ...  The  sun  is  by  far  the  most 
important  source  of  heat  for  the  soil.  When  its  rays  are  nearly 
vertical  there  is  tropical  heat ;  when  its  rays  are  withheld,  the  land 
is  locked  in  snow  and  ice.  The  heat  received  at  the  surface  passes 
downward  by  conduction."  l 

125.  Cultivation  of  the  soil.  —  A  moment's  thought  will 
convince  us  that  since  all  the  food  of  man  is  ultimately  de- 
rived from  plants,  any  measures  that  tend  to  improve  crops 
and  reduce  the  cost  of  crop 
production  are  of  vital  in- 
terest to  all  of  us.  In  the 
past,  before  much  was 
known  in  regard  to  scien- 
tific principles,  farmers 
put  their  seeds  in  the 
ground,  cultivated  them 

relatively  little,  and  trusted  Nature  to  do  the  rest.  In 
recent  times,  however,  man  has  learned  a  great  deal  in 
regard  to  soils,  crops,  and  methods  of  cultivation,  so  that 
the  modern  farmer  is  often  able  to  double  the  yield  of  a 
given  area.  The  investigations  of  the  National  and  State 
Departments  of  Agriculture  have  done  much  to  make  farm- 
ing a  science,  and  the  future  will  doubtless  see  far  greater 
improvements. 

For  the  cultivation  of  plants  the  first  requisite  is  a  suitable 
preparation  of  the  soil.  This  involves,  in  the  first  place, 
plowing,  which  turns  under  any  weeds  or  other  plants  that 
may  have  grown  there  before  and  which  prepares  for  the  work 
of  the  harrow,  an  implement  which  pulverizes  the  soil  so  that 

1  Bailey's  "Cyclopedia  of  American  Agriculture,"  Vol.  I,  "Farms," 
pp.  355,  356. 


114  PLANT  BIOLOGY 

ready  penetration  of  the  roots  of  the  growing  plant  is  possible. 
In  small  garden  plots  this  work  is  done  by  the  use  of  spades, 
hoes,  and  rakes.  It  is  often  found  necessary  to  add  well- 
rotted  manures  to  increase  the  humus  of  the  soil  and  chemi- 
cally prepared  fertilizers,  which  furnish  available  mineral 

food  for  the  crops.  We 
have  already  called  at- 
tention to  the  necessity 
of  proper  drainage  of 
the  soil  before  crops  are 
planted  (122).  Scien- 
tific investigation  has 
demonstrated,  too,  that 
frequent  and  thorough 

stirring  of  the  soil  is  most  important  not  only  to  prevent 
the  growth  of  weeds,  but  also,  and  this  is  even  more 
essential,  to  conserve  the  soil  moisture,  and  insure  proper 
aeration  of  the  roots.  It  has  been  found  that  it  is  possible 
to  produce  large  crops  on  semiarid  land  if  the  top-surface  of 
the  ground  is  kept  in  a  thoroughly  pulverized  condition. 
This  is  the  so-called  method  of  "  dry  farming." 

IV.   THE  STRUGGLE  FOR  EXISTENCE  AND  ITS  EFFECTS 

126.  Variation  among  plants.  —  We  have  all  heard  the  common 
expression  "as  nearly  alike  as  two  peas."  In  reality,  however, 
if  our  powers  of  observation  were  sharp  enough,  we  should  probably 
find  that  no  two  peas  are  exactly  alike  in  shape,  color,  size,  and 
weight.  The  plants  grown  side  by  side  from  any  two  peas  would 
also  vary  in  height,  in  number  and  position  of  leaves,  and  in  the 
number  and  vigor  of  flowers  and  seeds.  In  other  words,  as  every 
human  being  has  certain  distinguishing  characteristics,  so,  too,  we 
should  bear  in  mind  that  every  individual  plant,  however  small, 
shows  certain  differences  or  variations  from  every  other  individual 
of  its  class. 


PLANT  PROPAGATION 


115 


127.  The  numbers  of  seeds  produced  by  plants.  —  A  second  fact 
which  is  evident  to  all  is  that  plants  produce  an  enormous  number 
of  seeds.  Suppose  we  consider  the  case  of  a  vigorous  pea-vine.  In 
the  course  of  a  season  it  should  produce  at  least  20  pods,  each  con- 
taining at  least  5  seeds.  Hence,  at  the  end  of  a  single  season,  one 
pea  seed  would,  if  conditions  were  favorable,  have  multiplied  itself 
100  times.  If  each  one  of  these  seeds  were  to  be  planted  where  it 


FIG.  52.  —  Variations  in  the  corn  ears  produced  in  a  single  field.  —  (Courtesy 
of  Dr.  E.  M.  East,  Bussey  Institution,  Harvard  University.) 

had  plenty  of  moisture,  light,  food,  air,  and  favorable  temperature, 
it  likewise  should  give  rise  to  100  seeds,  and  so  at  the  end  of  the 
second  season  we  ought  to  have  100  X  100,  or  10,000  pea  seeds,  all 
propagated  from  a  single  pea  seed.  Simple  multiplication  shows  us 
that  at  the  end  of  five  years  a  moderately  prolific  plant  like  the 
garden  pea  would  have  given  rise,  had  all  conditions  been  favor- 
able to  10,000,000,000  new  seeds.  Bergen  has  made  a  patient 
count  of  the  number  of  seeds  produced  by  an  average  morning 
glory  plant,  and  finds  it  to  be  rather  more  than  3000 ;  hence, 
at  the  end  of  the  fifth  year,  if  such  a  rate  of  reproduction  were 


116 


PLANT  BIOLOGY 


to  be  continued,  there  would  be  243,000,000,000,000,000  morning 
glory  seeds.1 

It  is  evident,  however,  that  no  pea  vine  or  morning  glory  plant, 
if  left  to  itself,  would  be  able  to  produce  anything  like  the  number 
of  seeds  we  have  named,  for  otherwise  at  the  end  of  a  short  term  of 
years  there  would  not  be  room  on  the  whole  surface  of  the  globe  for 
any  other  kinds  of  plants  than  these.  As  a  matter  of  fact,  the  num- 
ber of  individuals  of  a  given  kind  of  organism  does  not  vary  much 
from  year  to  year.  In  the  first  place,  many  seeds  are  eaten  by  birds 
and  other  animals.  Again,  many  other  seeds  are  not  carried  to  a 
place  where  they  find  all  the  conditions  that  are  essential  for  germi- 
nation (118).  Still  other  seeds,  even  if  planted  in  good  soil 
and  in  favorable  surroundings,  fail  to  germinate.  Because  of  the 
great  losses  of  seeds  in  one  or  the  other  of  these  three  ways,  we  can 
get  some  idea  of  the  reason  why  plants  must  produce  a  great  abun- 
dance of  seeds  if  their  kind  is  to  be  perpetuated. 

128.  The  struggle  for  existence  among  plants.  —  But  even  if 
seeds  finally  germinate  and  get  a  foothold  on  the  soil,  a  great  many 


FIG.  53.  —  The  struggle  for  existence  and  the  survival  of  the  fittest  among 

turnips. 

of  the  plants  thus  started  will  never  reach  maturity  and  ripen  their 
seeds.     In  the  first  place,  each  plant  is  struggling  to  lift  up  its  leaves 

.          l  See  Bergen's  "Essentials  of  Botany"  (1910),  p.  202. 


PLANT  PROPAGATION 


117 


to  the  light  and  air,  and  those  that  are  most  vigorous  usually  get 
above  and  shade  the  others.  Again,  the  supply  of  water  and  mineral 
food  in  the  soil  of  a  given  area  is  limited ;  hence,  plants  that  cannot 
get  what  they  need  are  dwarfed  and  finally  starved  to  death.  In 


FIG.  54.  —  Charles  Darwin. 

the  third  place,  injurious  insects  destroy  an  enormous  amount  of 
vegetation,  the  loss  of  cultivated  crops  alone  from  this  cause  being 
estimated  at  $700,000,000  annually.  Frosts,  dry  seasons,  heavy 
rains,  and  fungous  diseases  are  other  important  factors  in  the  life 
of  many  plants.  And  so  if  we  were  able  to  see  what  is  actually 
going  on  in  each  square  foot  of  the  earth's  surface,  whether  of  forest, 


118 


PLANT  BIOLOGY 


field,  or  meadow,  we  should  doubtless  witness  a  life  and  death 
struggle  for  existence  (1)  between  individual  plants,  of  the  same 
kind,  (2)  between  individual  plants  of  different  kinds,  and  (3)  be- 
tween plants  and  animals. 

Charles  Darwin  in  his  great  book  on  the  "Origin  of  Species," 
published  in  1859,  —  a  book  which  has  doubtless  influenced  human 
thought  more  than  any  other  book  of  modern  times,  —  closes  his 
chapter  on  the  "Struggle  for  Existence"  with  the  following  words: 
"When  we  reflect  on  this  struggle  we  may  console  ourselves  with  the 
full  belief  that  the  war  of  nature  is  not  incessant,  that  no  fear  is 

felt,  that  death  is  gen- 
erally prompt,  and  that 
the  vigorous,  the 
healthy,  and  the  happy 
survive  and  multiply."1 

129.  The  survival  of 
the  fittest.  —  We  have 
seen  in  our  study  thus 
far  (1)  that  no  two  in- 
dividual plants  even  of 
the  same  kind  are  ex- 
actly alike,  (2)  that 
enormous  numbers  of 
seeds  are  produced  by 
plants,  and  (3)  that 
there  is  inevitable  com- 
petition or  struggle  for 
existence.  The  ques- 
tion, then,  that  con- 
fronts us  is  this :  Which 
of  the  many  competi- 
tors will  survive  in  the 
struggle,  reach  maturity,  and  finally  reproduce  themselves  ?  Obvi- 
ously those  individual  plants  that  vary  from  the  rest  in  such  a 


A. 


FIG.  55.  —  Dandelion  plant.  —  (Bailey.) 


Darwin's  "  Origin  of  Species,"  p.  72. 


PLANT  PROPAGATION  119 

way  that  they  can  best  adapt  themselves  to  their  surroundings. 
Let  us  see,  for  instance,  why  certain  weeds  like  the  dandelion  are 
so  common  a  nuisance  on  our  lawns.  In  the  first  place  these 
weeds  have  fleshy  roots  that  reach  deep  down  into  the  soil,  thus 
helping  the  plant  to  get  and  keep  a  stock  of  moisture  and  food. 
In  the  second  place  the  reserve  supply  of  nutrition  stored  in 
these  roots  enables  the  plants  to  put  forth  leaves  and  flowers  in 
early  spring,  and  so  to  get  a  good  start  ahead  of  their  com- 
petitors. Again,  their  short  stems  and  tough  leaves  can  be 
trampled  upon  without  killing  the  plant.  Insects  and  fungous 
diseases,  for  some  reason,  do  not  seem  to  attack  them.  And 
finally  dandelions  produce  a  large  number  of  tiny  seed-like 
fruits,  each  one  of  which  is  provided  with  a  delicate  tuft  of  hair 
which  a  puff  of  wind  will  carry  for  a  considerable  distance,  thus 
insuring  a  wide  dispersal  of  its  seeds.  In  nature,  then,  plants  like 
the  dandelion,  pigweed,  and  thistle  have  survived  in  the  struggle 
for  existence,  because  they  are  best  fitted  to  their  surroundings. 

V.  THE  IMPROVEMENT  OF  PLANTS  BY  MAN 

130.  Artificial  selection  of  favorable  variations.  —  In  the  pre- 
ceding pages  attention  was  frequently  called  to  the  fact  that  plants 
show  a  tendency  to  vary  more  or  less  from  each  other.  Now  it 
has  been  found  that  in  a  state  of  cultivation  this  tendency  becomes 
even  more  pronounced.  A  watchful  farmer  will  often  find  that  in 
his  cornfield  one  group  of  individuals  ripens  sooner  than  the  rest, 
and  so  if  he  wishes  to  sell  earlier  corn,  he  selects  and  plants  next  year 
corn  grains  derived  from  plants  that  have  varied  in  this  direction. 
Again,  he  may  notice  that  the  ears  on  certain  stalks  are  larger  and 
ripen  more  kernels  (see  Fig.  52) ;  these  the  crop-raiser  who  uses  his 
brains  would  select  for  seed  in  order  to  increase  his  yield  per  acre. 
Variations  in  many  other  directions  might  be  chosen  by  the  success- 
ful farmer  which  would  add  immensely  to  the  value  of  his  crops. 
It  is  estimated  that  if  every  farmer  were  to  select  his  seed  carefully, 
the  corn  production  in  the  United  States,  which  at  present  is  about 
$1,000,000,000,  in  a  short  time  would  be  increased  10  per  cent,  which 
would  add  $100,000,000  to  our  annual  income. 


120 


PLANT  BIOLOGY 


131.  Artificial  crossing  of  related  species.  —  Not  only  can  man 
secure  new  varieties  of  plants  by  watching  for  favorable  variations 
and  perpetuating  them  from  year  to  year,  but  he  can  actually  be 
instrumental  in  producing  new  kinds  of  plants.  This  process  is 
known  as  plant  breeding.  It  depends  fundamentally  on  the  prin- 
ciples we  learned  in  treating  of  cross-pollination  in  flowers.  Let 
us  illustrate  plant  breeding  by  the  following  account  of  the  work 
which  has  been  done  for  the  U.  S.  Department  of  Agriculture  by 
Dr.  H.  J.  Webber  of  Cornell  University.1 

In  the  winter  of  1894-1895  a  heavy  frost  destroyed  practically 
every  orange  tree  in  the  northern  and  central  part  of  the  State 

of  Florida.  The  loss  was  over 
$75,000,000.  The  problem  that 
confronted  the  orange  growers 
of  the  State  was  that  of  start- 
ing their  groves  anew  and  if 
possible  of  preventing  a  repeti- 
tion of  such  an  experience  by 
planting  a  more  hardy  kind  of 
orange  tree.  Dr.  Webber,  in 
casting  about  for  such  orange 
trees,  finally  chose  a  type  called 
the  trifoliate  orange  (Fig.  56) 
often  used  for  an  ornamental 
shrub,  and  one  that  would  not 
be  killed  by  winters  as  far  north 
as  Philadelphia.  The  fruit  of 
this  tree,  however,  is  small,  bitter, 
and  worthless  for  eating  pur- 
His  task,  therefore,  was 


FIG.    56.    —   Spray    from    trifoliate 
orange,  showing  leaves  and  fruit. 

to*  combine  the  characteristics  of 

a  juicy,  sweet-flavored  fruit  of  the  ordinary  Florida  orange  tree 
with  the  hardy,  cold-resistant  character  of  the  trifoliate  type.  He 
proceeded  in  this  fashion: 

1  See  Year-books  of  U.  S.  Department  of  Agriculture,  1904,  1905, 
1906. 


PLANT  PROPAGATION 


121 


From  the  flower-buds  of  one  type  of  orange  trees  he  removed  all 
the  stamens  before  blossoming  time,  and  then  covered  the  pistils 
with  paper  bags  to  prevent  the  visit  of  insects  bringing  pollen.  A 
second  set  of  buds  on  trees  of  the  other  type  were  likewise  covered 
with  paper  bags  to  prevent  possible  mixing  of  pollen  by  insect  visi- 
tors. When  the  stamens  of  one  kind  of  orange  blossoms  and  the 


TRtfOUfSTE 


FIG.  57.  —  Fruits  of  two  parent  plants  (orange  and  trifoliate)  at  left.  Six 
types  of  hybrid  fruits  (Rusk,  Willits,  783,  771,  772,  767)  developed 
by  cross-pollination  from  the  parent  plants,  all  being  good  fruits  except 
767,  which  proved  to  be  worthless.  Compare  seeds  and  pulp  in  various 
sections. 

pistils  of  the  other  kind  had  matured,  the  bags  were  carefully 
removed,  and  the  pollen  of  one  variety  was  dusted  over  the  pistil 
of  the  other  (see  87).  The  paper  bag  was  then  replaced  over 
the  artificially  pollinated  pistil,  and  the  latter  left  to  ripen.  Fruits 


122 


PLANT  BIOLOGY 


formed  by  the  cross-pollination  of  two  different  kinds  of  plants  are 
known  as  hybrid  fruits.  The  orange  hybrid  fruits  thus  developed 
were  sent  to  Washington,  where  the  seeds  were  removed  and  planted 
in  greenhouses.  When  the  young  hybrid  trees  were  about  a  foot 
high,  they  were  sent  to  Florida  and  grown  in  a  garden  of  the  Depart- 
ment of  Agriculture. 

After  a  great  many  experiments  in  crossing  the  two  kinds  of 
oranges,  and  after  rejecting  hundreds  of  plants  that  proved  to  be 
worthless,  Dr.  Webber  has  succeeded  in  producing  a  type  of  tree  that 
will  withstand  the  winters  of  regions  from  three  hundred  to  four 
hundred  miles  north  of  the  present  orange-growing  section  of  Flor- 
ida, and  which  will  also  produce  a  valuable,  juicy  fruit.  These 
new  fruits,  which  have  been  named  citranges,  make  a  delightful 
citrangeade  and  may  be  used  in  making  pies,  cakes,  marmalades, 
and  the  like.  In  a  similar  way  Dr.  Webber  has  produced  new 
varieties  of  tangerines,  pineapples,  cotton  plants,  and  grass  for  hay. 

The  work  of  Luther  Burbank1  in  California  has  likewise  resulted 
in  astonishing  colors  and  sizes  of  pinks  and  poppy  blossoms,  in 
plums  and  peaches  of  great  size,  and  in  entirely  new  plants  like  the 
"  pomato,"  produced  by  crossing  the  potato  with  the  tomato. 

132.    Some  of   the  valuable  crops  of  New  York  State.2 - 
New  York  ranks  first  of  all  the  States  of  the  Union  in  the 
production  of  the  following  crops : 


NAME  OF  CROP 

ANNUAL  VALUE 
OF  N.  Y.  CROP 

FRACTIONAL 
PART  OF 
U.  S.  CROP 

Hay      . 

$69,027,200 
20,996,900 
25,756,430 

i 

i 
* 

Potatoes 
Other  Veg 

stables    ...               . 

1  See  "New  Creations  in  Plant  Life,"  by  W.  S.  Harwood. 

2  The  authors  are  indebted  to  Professors  of  Cornell  University, 
for  the  use  of  the  figures  recently  compiled. 


PLANT  PROPAGATION 


123 


(Since  dairy  products  are  directly  dependent  on  agricultural 
conditions,  they  are  also  included  in  this  tabulation.) 


Dairy  Products 

$55  474  155 

i 

Milk 

36,284  833 

¥ 
i 

5 

In  spite,  however,  of  its  preeminence  among  the  States  in  the 
production  of  the  crops  just  named,  experts  tell  us  that  the  average 
yield  per  acre  throughout  the  State  is  probably  less  than  half  what 


FIG.  58.  —  Map  of  New  York  State,  showing  the  crops  grown  in  various 
areas.  —  (Courtesy  of  Prof.  E.  O.  Fippin,  of  Cornell  University.) 

it  should  be  or  might  be  if  more  intelligence  were  used  by  the  aver- 
age farmer.  The  following  quotation  from  an  investigation  made 
among  1303  of  the  farmers  in  the  vicinity  of  Cornell  University, 
near  the  center  of  the  State  of  New  York,  shows  in  a  striking  way 


124  PLANT  BIOLOGY 

the  commercial  advantage  of  even  a  high  school  education.  "Of 
the  owners,  those  who  went  only  to  district  school  made  an  average 
labor  income  of  $318.  The  average  labor  income  of  high  school 
men  was  $622.  Of  the  more  than  high  school  men  (i.e.  college, 
normal,  or  agriculture  courses)  it  was  $847.  The  differences  are 
emphatic.  The  labor  income  of  the  high  school  farmers  is  $304 
greater  than  that  of  the  district  school  men.  This  would  be  5  per 
cent  interest  on  $6080.  In  other  words  the  high  school  education 
of  a  farmer  is  equivalent,  on  the  average,  to  $6000  worth  of  5  per 
cent  bonds."  1 

133.    Summary   of   some   of  the   methods   employed   for 
increasing  crop  production.  —  The  farmers  of  the  future, 


A 

FIG.  59. —  A,  pile  of  corn  resulting  from  cross-pollination  ;  B,  pile  of  corn 
resulting  from  self-pollination.  —  (Bailey.) 

therefore,  to  be  successful  must  have  special  training.  They 
must  be  able  to  carry  on  selection  and  breeding  experiments, 
or  at  least  know  how  to  take  advantage  of  these  experiments 
in  the  choice  of  their  seeds ;  they  should  know  the  princi- 
ples involved  in  thorough  cultivation  and  in  the  application 
of  manures  and  fertilizers ;  they  should  determine  by  experi- 
ment the  type  of  crop  best  adapted  to  the  soil  of  their  farms, 
and  should  by  proper  rotation  of  crops  (that  is,  by  sowing 
clover  or  other  nitrogen-fixing  plants,  150,  one  year  and  corn 
the  next)  increase  the  fertility  of  their  soil.  If  a  farmer  is  a 
fruit  grower,  he  should  know  how  to  prune  properly,  and  he 

1  An  Agricultural  Survey  of  the  Townships  of  Ithaca,  Dryden, 
Danby,  and  Lansing,  published  by  Cornell  University,  1911. 


PLANT  PROPAGATION  125 

should  practice  grafting  to  develop  better  types  of  fruits.  If 
he  has  soil  adapted  for  woodland,  he  should  plant  forest 
trees,  and  put  into  effect  the  principles  of  forestry.  In  fact, 
there  are  countless  ways  in  which  the  farmer  of  the  future 
can  increase  the  yield  of  his  acres  if  he  but  mixes  brains  with 
the  labor  of  his  hands.  ; 


CHAPTER  IX 

PLANTS   IN   THEIR   RELATION   TO   HUMAN   WELFARE 

134.    Introduction.  —  Thus  far  in  our  study  of  plant  biology 
we  have  considered   the  principal   functions  carried  on  by 


FIG.  60.  —  Sweet  potato  plant. 

plants  and  have  observed  some  of  the  adaptations  of  struc- 
ture for  performing  these  functions.  We  have  proved,  for 
example,  that  plants  must  feed,  digest,  breathe,  and  carry 

126 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    127 


on  oxidation  in  order  to  live  and  grow,  and  must  reproduce 
their  kind  in  order  to  perpetuate  the  species.  We  turn  now 
to  a  discussion  of  some  of  the  uses  of  plants  to  man,  and  some 
of  the  ways  in  which  they  are  injurious. 

I.   SOME  OF  THE  USES  OF  PLANTS  TO  MAN 

135.  Uses  of  plants  for  food.  —  By  repeated  experiments 
we  have  proved  that  various  parts  of  plants  contain  generous 
stores  of  starch, 
sugar,  protein, 
and  mineral  mat- 
ters. In  our  study 
of  human  biology 
we  shall  find  that 
the  foods  which 
are  essential  for 
our  bodies  are 
composed  of  these 
same  substances. 
It  is  for  this 
reason  that  man 
and  other  animals 
are  so  largely 
dependent  upon 
plants  for  food. 
As  examples  we 
may  mention 
roots  like  pars- 


FIG.  61.  —  Coffee  tree.  Notice  coffee  berries  along 
sides  of  branches.  —  (Courtesy  of  New  York 
Botanical  Garden.) 


nips,      beets, 
and   sweet   pota- 
toes; stems,  like 
common  potatoes,  asparagus,  and  sugar  cane ;  leaves,  such 
as  cabbage  and  lettuce;    flowers,  for  example,  cauliflower; 


128 


PLANT  BIOLOGY 


fruits,  like  apples  and  peaches;  and  seeds  and  grains,  like 
beans,  wheat,  and  corn. 

136.   Suggestions  for  further   study  of  plants  used  as  food. — 

Study  No.  58.  (Optional.)  Visit  a  vegetable  market,  make  a  list 
of  the  various  plant  products  sold  for  food,  and  arrange  them  in 
a  table  as  follows : 


NAME  OF  FOOD 

PART  OF  PLANT  EATEN 

Root 

Stem 

Leaf 

Flower 

Fruit 

Seed 

String  beans 

X 

X 

Select  one  or  more  of  the  following  topics  for  special  study:  wheat, 
corn,  potatoes,  oats,  rice.  Consult  Bailey's  "  Cyclopedia  of  Ameri- 
can Agriculture,"  Vol.  II, "  Crops,"  any  encyclopedia,  or  the  publi- 
cations of  the  U.S. 
Department  of 
Agriculture.  De- 
termine (1 )  the  parts 
of  the  United  States 
(or  of  the  world) 
in  which  the .  crop 
is  raised  in  large 
quantity,  (2)  the 
amount  and  value 
of  a  year's  crop,  (3) 
methods  of  harvest- 
ing and  preparing 
the  crop  for  the 
FIG.  62.  —  Tea  plant.  —  (Bailey.)  market. 

137.  Uses  of  plants  for  flavoring  extracts,  beverages,  and 
medicines.  —  We  saw  in  a  previous  section  that  many  parts 
of  plants  are  available  for  use  as  food  by  man.  Because, 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE     129 


also,  of  the  presence  of  various  flavoring  compounds  in  plants, 
the  following  products  are  valuable.  .  For  instance,  vanilla 
extract  is  made  from  the  vanilla  bean,  pepper  from  pepper 
berries,  horse-radish  from  the  root  of  the  horse-radish  plant, 
and  ginger  from  an  underground  stem. 

We  are  dependent,  too,  upon  plants  for  many  beverages. 
The  coffee  berry  supplies  us  with  coffee,  tea  leaves  with  tea, 
and  from  the  pods 
and  seeds  of  the  cocoa 
tree  we  obtain  cocoa 
and  chocolate. 
Grapes  are  used  to 
make  wines,  from 
apples  cider  is  pre- 
pared, and  from 
grains  of  various 
kinds  other  alcoholic 
liquors  are  produced. 

Quinine,  the  well- 
known  remedy  for 
malaria,  was  formerly 
obtained  from  the 
bark  of  a  tree  known 
as  cinchona,  which 
grows  in  Peru.  This 
medicine  is  now  ob- 
tained almost  exclu- 
sively from  trees  cul- 
tivated in  India  and  other  Eastern  countries.  The  camphor 
tree  furnishes  camphor  gum ;  from  the  juice  of  poppy  fruits 
opium  and  morphine  are  obtained ;  whole  plants  like  pep- 
permint supply  us  with  valuable  medicines.  In  fact,  enormous 
numbers  of  drugs  are  prepared  from  various  parts  of  plants. 


FIG.  63.  —  Chocolate  tree.  —  (Courtesy  of  New 
York  Botanical  Garden.) 


130 


PLANT  BIOLOGY 


138.  Suggestions  for  further  study  of  parts  of  plants  used  as 
drugs.  —  Study  No.  59.  (Optional.) 

Visit  a  drug  store  or  consult  an  encyclopedia,  e.g.  Bailey's  "  Cyclo- 
pedia of  American  Agriculture,"  Vol.  II,  "  Crops,"  and  make  a  list 
of  common  drugs  obtained  from  plants.  Fill  out  in  your  note-book 
a  table  like  the  following: 


NAME  OF  DRUG 

PART  OF  PLANT  FROM  WHICH  IT  is  OBTAINED 

Root 

Stem 

Leaf 

Flower 

Fruit 

Seed 

Catnip      .     . 

X 

X 

139.  Uses  of  plants  for  clothing.  —  (Quoted  from  Bailey's 
"  Cyclopedia  of  American  Agriculture,"  Vol.  II,  "  Crops.") 
"  Fiber-producing  plants  are  second  only  to  food  plants  in 
agricultural  importance.  In  continental  United  States, 
however,  cotton,  hemp,  and  flax  are  the  only  fiber  plants 
cultivated  commercially;  and  aside  from  cotton  and  hemp, 
most  of  the  raw  fibers  used  in  our  industries  are  imported." 

"  The  cotton  of  commerce  is  the  hair  or  fiber  on  seeds  of  plants 
belonging  to  the  Mallow  family.  .  .  .  The  plants  are  mostly 
shrubby,  more  or  less  branching,  and  two  to  ten  feet  high.  .  .  . 
The  fruit  consists  of  three-  to  five-celled  '  bolls/  which  open  at 
maturity  through  the  middle  of  the  cells,  each  cell  liberating  seven 
to  ten  seeds  covered  with  long  fibers.  The  fiber  is  a  tubular  hair- 
like  cell,  Y^Vg-  to  -fifoy  of  an  inch  in  diameter,  somewhat  flattened 
and  spirally  twisted.  It  is  this  latter  characteristic  which  gives 
the  cotton  its  spinning  qualities.  .  .  . 

"  Picking  or  gathering  cotton  in  the  fields  is  a  heavy  item  of 
expense.  It  must  be  picked  by  hand,  as  no  mechanical  appliance  for 
harvesting  has  yet  been  invented  which  gives  satisfactory  results 
in  practical  working.  The  amount  of  cotton  that  one  person  can 
pick  in  one  day  varies  from  one  hundred  to  five  hundred  pounds, 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    131 


FIG. -64.  —  Cotton  picking. 

depending  on  the  skill  of  the  picker.  One  man  can  very  easily 
care  for  the  cultivation  of  twenty  acres  of  cotton,  but  it  requires 
two  to  four  pickers  to  harvest  such  a  crop  rapidly  enough  to  pre- 


132  PLANT  BIOLOGY 

vent  loss.  This  extra  labor  in  harvest  time  is  usually  supplied  by 
the  wives  and  children  of  the  laborers.  The  harvest  season  extends 
over  a  period  of  about  four  months,  beginning  August  15  to  Sep- 
tember 10,  according  to  locality. 

"  Cotton  is  probably  a  native  of  the  tropical  and  semi-tropical 
regions  of  both  hemispheres.  The  earliest  records  of  the  Asiatics 
and  Egyptians  speak  of  it ;  Columbus  found  it  growing  abundantly 
in  the  West  Indies,  while  other  early  explorers  found  it  growing 
in  Mexico  and  South  America.  .  .  .  There  is  no  region  in  the  world 
which  has  such  a  favorable  combination  of  suitable  land,  intelli- 
gent and  plentiful  labor,  cheap  capital  and  adequate  transportation 
facilities  for  the  cultivation  of  cotton  as  the  cotton  belt  of  the 
United  States.  It  has  been  the  chief  source  of  supply  of  the  cotton 
mills  of  the  world,  for  in  this  section  has  been  raised  several  times 
the  quantity  of  cotton  produced  in  all  other  countries  of  the  globe. 
There  are  various  other  countries  which  seem  to  possess  the  soil 
and  climatic  requirements  for  its  growth,  but  for  various  economic 
reasons  the  industry  has  not  been  greatly  developed  in  them ; 
however,  a  considerable  quantity  is  produced  in  the  following  coun- 
tries in  the  order  named:  India,  Egypt,  China,  Italy,  Turkey, 
Brazil,  West  Indies,  Mexico,  South  America,  Australia,  and  the 
South  Sea  Islands." 

140.  Further  study  of   fiber-producing   plants.  —  Study  No.    60. 
(Optional.)     Select  one  or  more  of  the  following  fiber-producing 
plants  for  further  study:  flax,  hemp,  jute,  raffia,  hat-straw.     Consult 
Bailey's  "  Cyclopedia  of  American  Agriculture,"  Vol.  II,  "  Crops," 
or  any  encyclopedia.     Determine  (1)  the  parts  of  the  United  States 
(or  of  the  world)  in  which  the  crop  is  raised  in  large  quantity,  (2) 
the  amount  and  value  of  a  year's  crop,  (3)  methods  of  harvesting 
and  preparing  the  crop  for  market.  '  * 

II.     THE  USES  OF  FORESTS  AND  FOREST  CONSERVATION 

141.  Uses  of  forests  for  fuel,  lumber,  and  other  commercial 
purposes.  —  In  the  earlier  days  of  our  country's  history  all 
the  fuel  for  heating,  for  running  locomotives  and  other  en- 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE     133 

gines  was  supplied  from  the  forests.  About  one  hundred  and 
fifty  years  ago,  coal  was  discovered  in  Pennsylvania,  and  one 
would  suppose  that  since  that  time  our  forests  would  have 
been  drawn  upon  less  heavily  for  fuel.  But  it  is  estimated 
that  the  United  States  burns  annually  at  the  present  time 
one  hundred  million  cords  of  wood.  While  we  are  consider- 
ing the  uses  of  plants  as  fuel,  we  should  remember  that  our 


FIG.  65. — A  view  showing  how  the  forests  of  the  Coal  Period  probably 
looked.  —  (Tarr  and  McMurry.) 

enormous  coal  beds  were  without  doubt  formed  from  great 
tree  ferns  and  other  plants  which  lived  in  bygone  ages.  Pe- 
troleum, too,  from  which  our  kerosene  oil  is  produced,  is 
believed  to  be  a  product  of  plant  decomposition. 

One  has  but  to  call  to  mind  the  enormous  use  of  trees  for 
framing  and  finishing  houses,  for  furniture,  for  railroad  ties, 
telephone  and  telegraph  poles,  for  shipbuilding,  and  for 
boxes,  barrels,  and  paper  manufacture,  to  realize  how  seem- 


134 


PLANT  BIOLOGY 


ingly  indispensable  are  forests.  When  the  early  settlers 
reached  this  country,  they  found  a  virgin  forest  covering  the 
whole  land.  Their  first  work  was  to  clear  1  and  in  order  to  get 
open  spaces  for  cultivation  and  as  a  means  of  protection 
from  attacks  of  the  Indians.  They  cut  down  the  trees  ruth- 
lessly and  the  timber  and  wood  which  was  not  needed  was  left 
to  decay  or  become  the  prey  of  forest  fires.  This  forest  de- 


FIG.  66.  —  Rock  containing  a  fossil  fern  which  grew  in  the  swamps  of  the 
Coal  Period.  —  (Tarr  and  McMurry.) 

struction  has  continued  even  to  our  own  day.  But  at  last 
men  are  beginning  to  see  that  unless  this  slaughter  of  our 
trees  is  stopped,  our  timber  supply  will  soon  be  gone.  In  fact, 
government  experts  tell  us  that  if  the  tree  areas  that  yet  re- 
main are  not  managed  according  to  a  different  system,  twenty 
years  hence  we  shall  reach  the  end  of  the  timber  supply  in  the 
United  States. 

142.   Further  study  of  forest  products.  —  Study  No.  61.     (Op- 
tional.)    Select  one  or  more  of  the  following  forest  products  for  fur- 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE     135 


FIG.  67.  — Wrong  methods  of  lumbering.  —  (Warren.) 


FIG.  68.  —  Right  method  of  lumbering.     Notice  carefully  piled  logs,  wood 
and  brush,  and  uninjured  young  trees. 


136  PLANT  BIOLOGY 

ther  study :  maple  sugar,  rubber,  tar,  turpentine,  wood  pulp,  alcohol, 
charcoal.  Consult  Bailey's  "  Cyclopedia  of  American  Agriculture," 
Vol.  II,  "  Crops,"  or  any  encyclopedia.  Determine  (1)  the  parts 
of  the  United  States  (or  of  the  world)  in  which  the  product  is 
obtained  in  large  quantity,  (2)  the  amount  and  value  of  a  year's 
crop,  (3)  methods  of  preparing  the  product  for  market. 

143.  Uses  of  forests  in  regulating  rainfall  and  flow  of 
streams.  —  We  turn  now  from  a  consideration  of  our  forests 
as  a  source  of  lumber  and  manufactured  products  to  a  dis- 
cussion of  their  effect  on  the  fall  of  rain  and  the  flow  of 
streams.  It  is  probably  true,  in  the  first  place,  that  the 
destruction  of  large  tracts  of  forest  lands  means  a  lessened 
rainfall,  at  least  so  far  as  local  showers  are  concerned.  We 
saw  in  our  study  of  the  functions  of  the  nutritive  organs  of  a 
plant  that  great  quantities  of  water  are  absorbed  by  the  roots, 
carried  up  through  the  woody  bundles  of  the  stem,  and  given 
off  through  the  stomata  of  leaves.  It  has  been  estimated 
that  a  single  oak  tree  of  average  size  gives  off  in  a  single 
season  over  one  hundred  and  twenty-five  tons  of  water.  If 
we  were  to  multiply  this  amount  by  the  number  of  trees  in  a 
forest,  we  would  get  some  idea  of  the  enormous  amount  of 
water  lifted  into  the  air  by  this  agency. 

Not  only  do  trees  help  to  produce  rain ;  they  also  conserve 
the  rain  when  it  falls  by  holding  it  in  the  soil,  and  preventing 
disastrous  floods.  Let  us  see  how  this  is  brought  about. 
When  the  raindrops,  fall  upon  the  tree  tops,  the  water  drips 
from  leaf  to  leaf,  and  finally  reaches  the  ground.  Here  it 
trickles  down  through  the  floor  of  the  forest,  which  is  formed 
of  thick  layers  of  decaying  leaves,  interlacing  roots,  and  earth 
particles  (see  frontispiece).  All  these  form  a  porous  sponge 
which  absorbs  and  holds  back  the  water.  Suppose,  now,  the 
trees  are  removed  from  the  hillsides.  When  the  rains  come, 
there  is  no  means  of  absorbing  the  water ;  instead,  it  flows 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    137 


rapidly  over  the  surface,  swelling  the  streams  into  torrents, 
which  bring  destruction  and  death  as  they  flood  the  valleys 
and  fields  along  their  course.  As  the  water  flows  over  the 
surface  of  the  land  from  which  the  trees  have  been  cut,  it 
carries  along  the  richest  part  of  the  soil,  thus  causing  loss  of 
fertility  in  the  uplands.  The  material  thus  carried  away 
fills  up  the  river  beds  and  harbor  mouths,  and  in  many  cases 
a  heavy  expense  is  entailed  in  its  removal. 

144.  Dangers  to  forests.  —  We  have  already  called  atten- 
tion to  the  threatened  destruction  of  our  American  forests 
by  careless  lum- 
bering. (See  141.) 
This  means  not 
only  the  whole- 
sale cutting  of 
large  areas  of 
trees,  but  the  lack 
of  forethought 
which  lumber- 
men show  in 
leaving  dead  tree 
trunks  and 
branches  to  become  the  prey  of  destructive  forest  fires, 
which,  when  once  started,  devastate  wide  areas.  The  annual 
loss  of  property  from  this  cause  is  conservatively  estimated 
at  more  than  one  hundred  million  dollars. 

This  forest  debris  of  dead  tree  trunks  and  branches  also 
furnishes  breeding  places  for  insects,  which,  when  hatched, 
prey  upon  healthy  trees.  Another  source  of  danger,  espe- 
cially to  young  forest  growth,  comes  from  permitting  large 
flocks  of  grazing  animals  like  cattle  and  sheep  to  feed  upon 
and  trample  down  the  small  trees.  If  we  are  to  preserve  the 


FIG. 


.  —  Excessive  erosion  of  land  caused  by  de- 
struction of  forests.  —  (Bailey.) 


138 


PLANT  BIOLOGY 


remnants  of  our  once  vast  forest  resources,  a  public  sentiment 
must  be  thoroughly  aroused  which  will  compel  the  passage 
and  enforcement  of  conservation  laws. 

145.    Necessity  for  reforesting  and  for  forest  protection.  — 

Surely,  enough  has  been  said  to  show  the  necessity  for  forest 

protection.  For- 
tunately, laws 
are  now  being 
passed  that  will 
enable  the  Na- 
tional and  some 
of  the  State  gov- 
ernments to  ac- 
quire large  tracts 
of  land  for  forest 
reservations.  In 
many  States 
these  forest  areas 
will  protect  the 
sources  of  large 
streams.  There 
is  great  need  of 
trained  experts 
who  will  go 
through  the  for- 
ests, mark  the 
trees  which  are 
mature  enough 

to  be  cut,  and  decide  which  way  they  should  fall  to  do 
the  least  damage  to  the  younger  growth.  Again,  large  areas 
now  devastated  should  be  replanted  with  young  forest  trees, 
and  this  is  also  being  done  to  a  considerable  extent.  In  many 


FIG.  70.  —  Planting  young  trees  on  hillsides. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    139 

foreign  countries,  notably  in  Germany,  the  forests  are  so 
used  that  year  after  year  they  supply  the  requisite  timber, 
and  still  continue  to  do  their  much  needed  work  in  conserv- 
ing the  rainfall.  Such  must  be  the  policy  in  our  country 
if  we  wish  to  escape  most  disastrous  penalties  that  always 
result  from  forest  destruction. 

Another  method  of  forest  protection  is  that  afforded  by 
cutting  trees  in  such  a  way  as  to  form  long,  treeless  strips  of 
land  known  as  fire  lanes.  Systems  of  telegraphic  communi- 
cation from  one  part  of  the  forest  reserves  to  another  and  fire 
wardens  are  necessary  factors  in  efficient  protection  of  forests. 

III.     FUNGI   AND    THEIR   RELATION   TO    HUMAN    WELFARE 

146.  Fungi.  —  Thus  far  we  have  confined  our  attention  to 
plants  which  are  easily  visible  to  the  naked  eye  and  which 
consist  of  roots,  stems,  and  leaves.  While  we  ordinarily 
think  of  these  as  the  common  plants,  in  reality  the  most 
common  plant  organisms  are  those  which  have  neither  roots, 
stems,  nor  leaves,  and  which  in  many  cases  are  microscopic 
in  size.  The  smallest  and  most  numerous  of  these  are  known 
as  bacteria,  which  are  found  all  about  us,  in  the  soil,  in  the  air 
we  breathe,  on  the  food  we  eat,  and  in  the  water  we  drink. 
Bacteria  belong  to  a  great  group  of  plants  called  fungi. 
All  fungi  are  characterized  by  the  absence  of  chlorophyll, 
hence  plants  of  this  group  cannot  manufacture  their  carbo- 
hydrate food  out  of  materials  from  the  soil  and  air,  but  are 
dependent  on  foods  made  by  green  plants.  More  familiar 
to  us,  perhaps,  than  bacteria  are  the  fungi  known  as  mush- 
rooms and  toadstools,  and  the  molds  and  mildews.  Still 
other  fungi  are  the  yeasts,  the  rusts,  and  the  smuts.  Because 
of  the  enormous  economic  importance  of  many  of  these  forms, 
we  shall  consider  more  or  less  in  detail  the  structure,  func- 
tions, and  life-history  of  several  of  them. 


140  PLANT  BIOLOGY 


A.   Bacteria1 

147.    Microscopical    appearance    and    size    of   bacteria.  — 

Every  one  is  familiar  with  the  fact  that  if  a  bouquet  of  flowers 
is  left  for  some  time  in  a  vase  of  water,  the  stems  decay  and 
disagreeable  odors  are  given  off.  This  is  a  common  example 
of  the  action  of  bacteria,  for  all  decay  is  due  to  the  work  of 
these  organisms.  When  we  come  to  examine  the  flower-stems 
or  the  putrid  water,  we  find  a  slimy  scum.  If  we  put  a  drop 
of  this  scum  on  a  slide,  coyer  with  a  cover-glass,  and  examine 
with  the  highest  powers  of  the  microscope,  usually  we  would 
see  many  different  forms  of  living  things.  Some  of  them 
would  probably  appear  relatively  large,  and  these,  as  we  shall 
see  later  (Chapter  IV, ' '  Animal  Biology  ") ,  are  single-celled  ani- 
mals. A  closer  examination  will  disclose  countless  numbers 
of  very  minute,  colorless  organisms ;  these  are  the  bacteria. 
A  careful  study  of  many  kinds  of  bacteria  shows  that  they  have 
several  characteristic  shapes  (see  Fig.  71)  by  means  of  which 
they  can  be  roughly  classified.  Some  are  rod-shaped  (like  a 
firecracker),  some  are  spherical,  or  egg-shaped,  and  still  others 
are  spiral-shaped.  Each  bacterium  is  a  tiny  bit  of  translucent 
protoplasm,  inclosed  in  a  cell  wall  of  cellulose.  Thus  far  no 
nucleus  has  been  discovered  in  any  kind  of  bacteria.  Be- 
cause of  their  cellulose  walls,  and  because  of  their  likeness 
to  certain  low  forms  of  green  plants,  biologists  now  regard 
these  organisms  as  plants  rather  than  animals. 

Some  of  the  rod-shaped  bacteria  have  one  or  more  long, 
hairlike  projections  from  the  ends,  called  cil'i-a,  which  give 
the  germs  still  further  resemblance  to  firecrackers.  These 
cilia  lash  about  rapidly,  and  thus  drive  the  cells  through  the 

1  Because  of  the  importance  of  bacteria  in  relation  to  sanitation, 
it  may  be  found  advisable  to  consider  this  whole  topic  in  connection 
with  human  biology.  Sections  148-154  will  therefore  be  repeated 
in  the  book  on  human  biology. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    141 


water.  The  spiral  bacteria  roll 
over  and  over,  and  advance  in  a 
spiral  path  like  a  corkscrew.  Other 
forms  have  rapid  movements,  but 
it  is  not  known  how  they  are  ac- 
complished. 

It  is  very  difficult  to  get  any 
clear  notion  of  the  extreme  minute- 
ness of  bacteria.  It  means  but 
little  to  say  that  the  rod-shaped 
forms  are  -5^517  of  an  inch  in  length. 
The  imagination  may  be  somewhat 
assisted  if  we  remember  that  fifteen 
hundred  of  them  arranged  in  a 
procession  end  to  end  would 
scarcely  equal  the  diameter  of  a 
pin  head. 

148.  Reproduction  of  bacteria. 
—  When  conditions  are  favorable, 
the  production  of  new  cells  goes 
on  with  marvelous  rapidity.  The 
process  is  something  as  follows : 
The  tiny  cells  take  in  through  the 
cell  wall  some  of  the  food  materials 
that  are  about  them,  change  this 
food  into  protoplasm,  and  thus 
increase  somewhat  in  size.  The 
limit  is  soon  reached,  however,  and 
the  bacterium  begins  to  divide 
crosswise  into  halves.  The  mother 
cell  thus  forms  two  daughter  cells 
by  making  a  cross  partition  (cell  wall  of  cellulose)  between  the 
two  parts.  (See  Fig.  71,  C.)  If  the  daughter  cells  cling  to- 


FIG.   71.  —  Various    forms 
bacteria. 

A,  a  colony  of  spherical  bac- 
teria (coccus,  plur.  cocco)  ; 
B,  rod-shaped  bacteria  (ba- 
cillus, plur.  bacilli)  ;  C,  rod- 
shaped  bacteria  dividing ; 
D,  rod-shaped  bacteria,  each 
containing  a  spore  ;  E,  spiral 
bacteria  (spirillum,  plur. 
spirilla)  each  with  cilia. 


142  PLANT  BIOLOGY 

gether,  a  chain  or  a  mass  is  formed.  Oftentimes  they  separate 
entirely  from  each  other.  In  either  case  the  whole  mass  of 
bacteria  is  called  a  colony. 

It  usually  takes  about  an  hour  for  the  division  to  take  place. 
Suppose,  then,  we  start  at  ten  o'clock  some  morning  with  a 
single  healthy  bacterium.  If  conditions  are  favorable,  there 
would  be  two  cells  at  eleven  o'clock,  and  by  twelve  o'clock 
each  of  these  two  daughter  cells  would  form  two  granddaugh- 
ter cells ;  the  colony  would  then  number  four  individuals. 
Should  this  process  continue  for  twenty-four  hours,  or  until 
ten  o'clock  on  the  day  after  the  single  bacterium  began  its 
race,  the  colony  would  number  16,777,216  bacteria.  "  It 
has  been  calculated  by  an  eminent  biologist,"  says  Dr. 
Prudden,1  "  that  if  the  proper  conditions  could  be  maintained, 
a  rodlike  bacterium,  which  would  measure  about  a  thou- 
sandth of  an  inch  in  length,  multiplying  in  this  way,  would  in 
less  than  five  days  make  a  mass  which  would  completely  fill 
as  much  space  as  is  occupied  by  all  the  oceans  on  the  earth's 
surface,  supposing  them  to  have  an  average  depth  of  one  mile." 

149.    Necessary  conditions  for  the  growth  of  bacteria.  — 

Such  startling  possibilities  as  those  suggested  in  the  preceding 
section  fortunately  can  never  become  realities,  for  the 
favorable  conditions  to  which  we  have  referred  soon  cease  to 
exist.  Bacteria,  like  all  other  living  organisms,  require  food, 
oxygen,  moisture,  and  a  certain  degree  of  warmth.  Let  any 
one  of  these  conditions  be  withheld,  and  the  cells  either  die 
or  cease  to  be  active.  Sometimes,  when  food  or  moisture 
begins  to  fail,  the  protoplasm  within  each  cell  rolls  itself 
into  a  ball  and  covers  itself  with  a  much  thickened  wall. 
This  protects  it  until  it  again  meets  with  conditions  favorable 
for  growth.  The  process  we  have  been  describing  is  known  as 

1  "  The  Story  of  the  Bacteria,"  by  Dr.  T.  Mitchell  Prudden.  G.  P. 
Putnam's  Sons,  New  York. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    143 


spore  formation;  the  tiny  protoplasmic  sphere  is  called  a  spore, 

and  its  dense  covering  a  spore  wall.     (Fig.  71,  D.)     In  this 

condition     bacteria    may    be    blown 

hither  and  yon  as  a  part  of  the  dust. 

They  may  be  heated  even  above  the 

temperature  of  boiling  water  without 

being    killed.     When  at   length   they 

settle  down  on  a  moist  surface  that 

will  supply  them  with  food,  the  spores 

burst    their    thick    envelope,    assume 

once  more  their  rod-shaped  or  spiral 

form,  and  go  on  feeding,  assimilating, 

and  reproducing  their  kind. 

150.  Relation  of  bacteria  to  soil 
fertility. — Having  discussed  somewhat 
the  structure  and  functions  of  bacteria, 
we  are  now  to  consider  the  great  im- 
portance of  these  microscopic  organ- 
isms to  human  welfare.  In  the  first 
place,  were  it  not  for  their  never  end- 
ing activity,  all  life  upon  the  earth 
would  soon  cease  to  exist.  Let  us  see 
why  this  is  so.  When  animals  or  plants 
die,  their  bodies  fall  upon  the  ground, 
and  were  these  lifeless  masses  not  taken 

FIG.   72. —  Roots   of   horse 

care  of,  the  whole  surface  of  the  earth  bean,  showing  numerous 
would  long  since  have  been  covered 
with  a  vast  number  of  unburied  or- 
ganisms. All  this  dead  material,  however,  as  we  have  seen, 
is  food  for  the  countless  bacteria;  they  cause  it  to  decay, 
and  thus  decompose  it  into  simpler  chemical  compounds 
that  can  soak  into  the  earth  and  then  be  used  in  the  nu- 


144  PLANT  BIOLOGY 

trition  of  the  higher  plants.  And  since  plants  are  con- 
stantly taking  from  the  soil  the  food  materials  which  they 
need,  this  soil  would  tend  to  become  less  and  less  fertile 
were  it  not  for  the  work  of  the  bacteria  that  caused  de- 
composition. This  is  the  reason  why  rotting  manure  adds 
to  the  fertility  of  soil. 

Again  it  has  been  proved  that  certain  kinds  of  bacteria 
directly  increase  the  amount  of  nitrogen  compounds  that  are 

so  essential  for  plant 
growth.  It  has  long 
been  known  that  corn 
and  other  crops  will  grow 
better  in  soil  that  has 
just  borne  a  crop  of  peas, 
beans,  clover,  or  other 
members  of  the  pea 
family.  Within  recent 
years  an  explanation  of 
this  fact  has  been  found. 
When  the  roots  of  those 

FIG.  73.- Bacteria  from  root-tubercles.-    P°d-bearing     plants     are 

(Duggar.)  examined,  small  swellings 

are  seen.     These  contain 

multitudes  of  bacteria  that  are  able  to  take  the  free  nitrogen 
from  the  air,  where  it  exists  in  such  abundance,  and  store  it 
away  in  the  form  of  nitrates  which  are  very  important  mineral 
matters  needed  by  all  crops.  Since  those  bacteria  can  be  put 
into  soils  that  do  not  have  them,  it  may  be  possible  in  the 
near  future  to  restore  much  of  the  fertility  which  has  been  lost. 

161.  Relation  of  bacteria  to  the  flavors  of  food.  —  Again, 
many  of  the  flavors  of  food  are  due  to  the  action  of  bacteria. 
Meats,  for  instance,  when  freshly  killed,. are  tough  and  taste- 
less. If  allowed  to  stand,  however,  by  the  decomposing 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    145 

action  of  bacteria  these  meats  become  tender  and  acquire 
their  distinctive  flavors.  A  similar  action  takes  place  when 
butter  or  cheese  ripens,  and  the  dairy  industry  has  been  per- 
fected to  such  a  degree  that  bacteria  of  certain  kinds  have 
been  proved  to  give  rise  to  definite  flavors,  and  these  bacteria 
can  be  produced  in  pure  cultures  for  the  dairymen. 

152.  Bacteria  in  the   industries.  —  Without  the  help  of 
bacteria  the  preparation  of  linen,  jute,  and  hemp  would  be 
impossible.     All   these   valuable   products   are   plant  fibers 
which  are  connected  with  woody  materials  so  closely  that  they 
cannot  be  separated  without  first  subjecting  the  stems  of 
flax,  hemp,  and  jute  to  a  process  of  decay  in  large  tanks  of 
water.     Moisture  and  warmth  induce  the  rapid  growth  of 
germs,  and  this  process  loosens  the  tough  fibers  so  they  can 
be  separated  from  the  useless  parts  of  the  plant. 

The  change  of  alcohol  into  vinegar  is  caused  by  bacteria. 
Likewise  in  the  preparation  of  indigo  other  forms  of  bacteria 
are  all  important. 

153.  Bacteria  as  the  foes  of  man.  —  Unfortunately,  how- 
ever, there  are  certain  germs  that  find  favorable  conditions 
for  growth  only  in  living  animal  tissue.     Thus  the  bacterium 
of  consumption  grows  in  the  lungs,  the  germ  of  diphtheria  in 
the  throat,  and  the  bacteria  that  cause  typhoid  fever  in  the 
intestines.     These  disease-producing  germs  are  called  by  Dr. 
Prudden  "  man's  invisible  foes."     Yet  wonderful  progress  is 
being  made  in  the  fight  against  them.     We  have  learned  how 
to  check  the  ravages  of  cholera,  typhoid,  and  diphtheria,  and 
even  consumption  is  found  to  be  a  preventable  disease. 
Further  discussion  of  bacteria  will  be  found  in  several  of  the 
subsequent  chapters.1 

1  For  laboratory  work  on  bacteria,  see  Chapter  II,  "  Human  Bi- 
ology."   Also  consult  Peabody's  "  Laboratory  Exercises  in  Anatomy 
and  Physiology"  (1902),  pp.  100-107. 
L 


146 


PLANT  BIOLOGY 


B.   Yeast  (Optional) 

154.  Microscopical  appearance  and  size  of  yeast.  —  A  small 
piece  of  a  cake  of  compressed  yeast,  mixed  in  a  spoonful  of  water, 
forms  a  milky  fluid  that  is  much  like  so-called  bakers'  or  brewers' 
yeast.  If  we  examine  with  the  microscope  a  bit  of  this  mixture 
in  the  same  way  in  which  the  bacteria  were  studied,  we  find  that  it 
consists  of  innumerable  bodies  of  minute  size.  These  are  yeast 
cells.  Each  cell  is  more  or  less  egg-shaped,  and  is  composed  of  color- 
less protoplasm  inclosed  within  a  wall 
of  cellulose.  By  the  use  of  special 
stains,  a  nucleus  becomes  visible. 
(The  spherical  dots  seen  in  fresh  yeast 
cells  are  known  as  vacuoles  and  are 
filled  with  a  colorless. liquid.)  Yeast, 
like  bacteria,  is  regarded  as  one  of  the 
lowest  forms  of  plant  life. 

155.    Reproduction  of  yeast.  —  Most 
of  the   cells  that  we   are  looking  at 
are  not  separate  individuals,  but  are 
FIG.  74.  — Yeast  cells,  showing  strung  together  in  little  chains.     This 

S±f.tT5Sit:JS fact  leads  us  to  a  disc™  of  the 

shown.    Clear  spaces  are  vac-  method  of  reproduction  of  yeast.   When 
uoles.  there  is  a  sufficient   supply  of  food, 

moisture,  and  oxygen,  and  when  the  temperature  is  favorable, 
these  living  plant  cells  begin  to  feed  and  to  grow.  They  soon  reach 
their  full  size,  and  then  the  cell  wall  is  pushed  out  at  the  side  by  the 
growing  protoplasm.  In  this  way  a  bud  is  formed.  This  continues 
to  grow  and  soon  becomes  a  daughter  cell,  closed  off  from  the  mother 
cell  by  a  wall  of  cellulose.  Meanwhile,  one  or  more  buds  may  be 
forming  on  the  outside  of  the  daughter  cells.  If  all  these  cells 
cling  together,  a  colony  is  formed  which  consists  of  a  mother  cell 
(largest  in  size),  one  or  more  daughter  cells,  and  several  tiny  grand- 
daughter cells.  The  individual  cells  are  easily  separated  from  one 
another.  This  method  of  reproduction  is  known  as  budding  (Fig.  74) . 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    147 

156.  Changes  caused  by  yeast.  —  A  yeast  mixture  may  be  easily 
prepared  for  experimentation  by  pouring  into  a  jar  a  cup  of  water, 
adding  a  spoonful  of  molasses,  and  a  spoonful  of  the  milky  fluid 
made  as  described  in  154. 

If  the  jar  with  its  contents  is  set  aside  in  a  warm  place  (70°  to 
90°  F.)  for  a  short  time,  it  begins  to  "work,"  and  bubbles  of 
gas  rise  to  the  surface.  At  the  end  of  several  hours,  we  notice 
that  the  sweetness  of  the  molasses  is  disappearing,  that  the  mixture 
begins  to  smell  sour,  and  that  a  sharp,  biting  taste  is  becoming  evi- 
dent. All  these  changes  are  caused  by  the  growth  of  living  yeast 
cells. 

Now,  what  is  the  gas  that  is  formed  in  this  process,  and  what 
causes  the  changes  in  taste  and  odor?  To  answer  these  questions 
we  must  carry  our  experiments  still  further.  When  the  mixture 
is  "  working  "  well,  the  bottle  should  be  tightly  closed  with  a  rubber 
stopper,  through  which  extends  one  arm  of  an  inverted  U-shaped 
tube.  The  other  end  of  this  tube  should  run  over  to  the  bottom 
of  a  test  tube  half-filled  with  limewater.  The  gas  that  has  been 
rising  through  the  yeast  mixture  now  passes  through  the  U-tube, 
and  as  it  comes  in  contact  with  the  limewater,  the  latter  changes  to 
a  milky-white  color.  This  proves  that  the  gas  formed  during  the 
growth  of  yeast  is  carbon  dioxid. 

After  "  working  "  a  day  or  two,  the  yeast  mixture  will  have  a 
strong  taste  and  odor.  A  part  of  it  should  then  be  poured  into  a 
glass  Florence  flask  (commonly  used  in  the  chemical  laboratory 
for  boiling  liquids),  and  the  mouth  should  be  closed  by  a  rubber 
stopper.  The  short  arm  of  a  long  delivery  tube  should  be  passed 
through  this  stopper.  When  the  flask  is  heated  gently,  some  of  the 
liquid  is  changed  to  a  vapor.  If  the  delivery  tube  is  cooled  by  cov- 
ering it  with  cloths  wet  in  cold  water,  the  vapor  condenses  into  a 
liquid,  which  comes  from  the  end  of  the  tube  in  drops.  This  opera- 
tion we  have  been  describing  is  known  as  dis-til-la'tion.  In  distilling 
a  liquid,  we  first  convert  it  into  a  vapor,  and  then  condense  this  vapor 
into  a  liquid.  After  collecting  a  few  spoonfuls,  the  liquid  should  be 
slowly  distilled  a  second  time.  Then  we  obtain  a  colorless  fluid 
that  has  the  distinct  smell  and  taste  of  alcohol.  It  burns,  too,  with 


148  PLANT  BIOLOGY 

a  pale  blue  flame.  And  so  we  learn  that  yeast,  as  it  grows  in  the 
molasses  mixture,  changes  the  sweet  substances  into  carbon  dioxid  and 
alcohol,  a  process  that  is  known  as  alcoholic  fer-men-taftion. 

157.  Uses  of  yeast.  —  When  bread  is  made,  water  (or  milk), 
butter,  salt,  sugar,  and  yeast  are  added  to  flour.  After  the  mixture 
has  been  stirred  together,  a  sticky  mass  of  dough  is  formed,  which 
in  a  warm  place  begins  to  rise.  This  is  due  to  the  fact  that  the  yeast 
cells  change  the  sugar  into  alcohol  and  carbon  dioxid.  Bubbles  of 
gas  are  thus  imprisoned  in  the  sticky  dough.  While  expanding  and 
seeking  to  escape,  they  make  the  solid  mass  porous.  After  the  bread 
has  risen  sufficiently,  it  is  kneaded  in  order  to  break  up  the  large 
bubbles  and  in  order  to  distribute  the  gas  throughout  the  dough. 
When  the  bread  is  baked,  the  alcohol  and  carbon  dioxid'  pass  off 
into  the  air,  leaving  the  bread  light  and  digestible.  These  minute 
organisms  are  also  of  great  commercial  importance  in  the  manufac- 
ture of  alcohol  and  of  all  kinds  of  liquors.  It  is  known  that 
yeast  cells  are  found  commonly  in  the  air.  As  different  kinds  of 
fruits  ripen,  they  are  usually  more  or  less  covered  with  yeast  or 
its  spores.  When,  therefore,  grapes  are  gathered  and  their  juice  is 
pressed  out,  the  sweet  liquid  is  soon  alive  with  the  busy  cells,  and 
fermentation  begins  at  once.  In  this  way  wines  are  produced. 
Cider  is  produced  by  the  fermentation  of  apple  juice. 

In  the  manufacture  of  beer  and  of  other  malt  liquors,  barley  is 
commonly  used.  The  grain  is  soaked  and  allowed  to  sprout  for 
a  short  time,  until  the  starch  is  changed  to  grape  sugar.  The  barley 
kernels  are  then  killed  by  heat  to  prevent  further  changes,  and  the 
grain  is  then  known  as  malt.  When  this  is  put  into  water,  the  sugar 
is  extracted.  Yeast  is  then  added,  and  the  mass  ferments.  The 
beer  thus  formed  contains  2  to  5  per  cent  of  alcohol. 

Distilled  liquors,  or  spirits,  are  obtained  from  wines  and  other 
fermented  liquors  by  the  process  of  distillation,  the  principles  of 
which  have  already  been  explained.  Brandy  is  made  by  distilling 
wine,  whisky  is  obtained  from  fermented  corn  and  rye,  and  rum  is 
manufactured  from  molasses.  All  of  these  liquors  contain  a  large 
percentage  of  alcohol  (40  to  50  per  cent). 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    149 

158.  Suggestions  for  laboratory  work  on  yeast.  —  No.  62. 
Students  should  examine  the  appearance  of  yeast  cells  under  the 
low  and  high  powers  of  the  compound  microscope.  If  time  permits, 
the  demonstration  of  carbon  dioxid  production  and  of  distillation 
of  alcohol  might  well  be  made.  (See  Peabody's  "  Laboratory  Exer- 
cises," pp.  94-99,  Henry  Holt  &  Co.,  New  York  City.) 


C.   Bread  Mold  (Optional) 

169.    Structure  of  bread  mold.  —  If  pieces  of  bread  or  cake  be 
moistened,  and  placed  in  a  dish,  and  covered  with  a  bell- jar  in  the 


FIG.  75.  —  Bread  mold,  showing  nutritive  hyphae  (A) ;  reproductive  hyphae 
CB) ;  and  spore  cases  (C).  —  (Osterhout.) 


dark,  in  a  few  days  grayish  patches  will  appear  in  places  on  the 
surface  of  the  bread.  This  growth  is  due  to  the  activity  of  one 
of  the  fungi,  known  as  a  mold,  and  will  probably  be  the  kind 
called  bread  mold.  No  care  is  required  to  produce  the  plant  in 
quantities ;  on  the  contrary,  as  common  experience  shows,  some 
pains  must  be  taken  by  the  housekeeper  to  prevent  it  from  spoil- 
ing food. 

When  the  bread  mold  is  examined  with  a  hand  lens,  it  is  seen  to 


150  PLANT  BIOLOGY 

consist  of  a  mass  of  fine  interlacing  threads  called  the  mycelium. 
(See  Fig.  75.)  Single  threads  are  known  as  hyphce. 

160.  Reproduction  and  life  history  of  bread  mold.  —  Some  of 
the  hyphse  in  their  growth  assume  an  upright  position,  and  each  of 
these  at  the  upper  end  develops  a  little  globular  white  mass  or  spore 
case.    (See  Fig.  75.)    An  examination  with  the  high  power  of  the 
microscope  shows  that  the  spore  cases  are  filled  with  tiny  cells 
known  as  spores.     When  the  spores  are  ripe,  the  spore  cases  appear 
brown  or  black,  they  break  open,  and  the  spores  are  scattered. 
If  these  spores  fall  on  food  of  some  kind,  such  as  bread,  they  begin 
to  germinate,  and  each  one  produces  another  mass  of  threads  with 
spore  cases  on  erect  hyphaB.     In  other  words,  the  mold  produces 
spores  and  the  spores  reproduce  the  mold.     The  spores  of  molds 
are  in  the  air  nearly  everywhere,  hence  we  see  why  molds  appear 
so  quickly  on  foods  of  various  kinds,  provided  they  are  moist  and  in 
a  warm  place. 

161.  Nutrition  in  the  fungi.  —  Molds,  like  other   fungi,  as   we 
have  already  said,  cannot  manufacture  their  own  food  out  of  the 
materials  obtained  from  the  soil  and  air,  but  are  dependent  on  foods 
made  by  green  plants.     Certain  of  the  threads  called  the  nutritive 
hyphce  form  ferments  which  digest  the  food  compounds  found  in 
bread  or  other  substances  on  which  the  mold  is  growing,  and  then  the 
digested  food  is  absorbed,  used  in  growth,  and  in  the  production  of 
energy.    Other  threads  develop  the  spore  cases  and  so  are  called  re- 
productive hyphce.    Hence,  it  is  evident  that  fungi,  like  all  plants,  carry 
on  both  nutritive  and  reproductive  functions,  but  on  account  of  the 
lack  of  chlorophyll  are,  like  animals,  dependent  on  the  green  plants 
for  their  supply  of  food. 

162.  Suggestions   for  laboratory  work   on  bread   mold.  —  No. 

63.  Sow  bread  mold  as  suggested  in  159  in  sufficient  quantity 
to  supply  each  two  pupils  with  a  piece  of  the  moldy  bread.  Pupils 
should  examine  a  specimen  with  a  hand  magnifier,  describe  the 
appearance  of  the  mycelium  and  hyphae  bearing  spores,  and 
should  then  make  a  drawing  to  show  these  points.  Some  of  the 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    151 

spore  cases  should  be  placed  on  a  slide  in  water  and  covered  with  a 
cover  glass.  If  the  glass  cover  is  tapped  with  a  pencil,  some  of  the 
spore  cases  will  be  ruptured.  The  preparation  should  then  be  ex- 
amined with  the  high  power  of  the  compound  microscope,  and  the 
ruptured  spore  cases  drawn,  together  with  a  few  of  the  escaping 
spores. 

D.    Other  Fungi  (Optional) 

163.    Mushrooms.  —  Mushrooms  are  forms  of  fungi  which  are 
often  called    "  toadstools,"    especially  if   they  are    supposed   to 


FIG.  76.  —  An  edible  mushroom. 

be  poisonous.  All  fungi  of  this  kind  should,  however,  be  called 
mushrooms,  since  their  structure  and  life  history  are  similar.  The 
conspicuous  part  of  the  plant,  the  umbrella  shaped  structure  so 
familiar  to  all,  is  really  the  reproductive  organ  of  the  plant,  the  part 
that  bears  the  spores  (Fig.  76).  The  nutritive  organs  are  a  mass  of 
threads  (as  in  the  mold)  which  lie  beneath  the  surface,  where  they 
absorb  the  foods  from  some  decaying  material  in  the  soil  to  give 
rise  to  the  reproductive  body. 


152 


PLANT  BIOLOGY 


As  indicated  above,  many  mushrooms  are  poisonous,  but  a  few 
kinds  are  known  to  be  edible.1  Mushrooms  are  not  especially  nu- 
tritious ;  that  is,  they  cannot  take  the  place  of  the  cereals  and  other 
staple  foods,  but  they  serve  to  add  to  the  variety  of  materials  which 
are  more  valuable  for  their  flavoring  qualities  than  for  the  quantity 
of  nutriment  they  contain.  Commercially  the  cultivated  mush- 
room is  of  considerable  importance,  especially  in  Europe.  Paris 
is  said  to  be  the  center  for  the  sale  of  this  product.  In  the  year 

1901  it  was  estimated  that  10,000,000 
pounds  of  cultivated  mushrooms 
passed  through  the  markets  of  Paris. 
In  this  country  the  mushroom  is  of 
CDmmercial  importance  only  in  the 
regions  of  the  larger  cities. 

164.  Rusts  and  smuts.  —  The 
fungi  known  as  rusts  receive  their 
name  from  the  rusty  appearance  in 
an  early  stage  of  their  growth  which 
they  cause  on  the  stems  and  leaves 
of  plants  which  they  attack.  The 
cereals,  wheat,  oats,  barley,  and  rye, 
are  the  crops  which  this  fungus  in- 
jures most.  In  the  case  of  wheat, 
half  of  the  crop  or  even  more  may 
be  destroyed. 

The  very  suggestive  name  of  smut 
is  given  to  another  fungus  which 

affects  all  the  cereals  named  above,  and  corn  as  well.  In  the  case 
of  corn,  this  plant  often  affects  the  ears  as  well.  The  name  is 
probably  given  on  account  of  the  appearance  of  the  mass  of  black 
spores.  If  one  touches  these  spores,  especially  those  of  corn  smut, 
with  the  finger,  and  then  rubs  the  finger  on  some  white  paper  or 

1  So  many  deaths  are  caused  by  using  poisonous  instead  of  edible 
mushrooms  that  it  is  never  safe  to  eat  wild  forms  until  they  have 
been  identified  by  an  expert. 


FIG.  77. —  Corn  smut  on  an  ear 
of  corn. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    153 

cloth,  a  sooty  mark  is  left.  The  damage  done  by  smuts  is  very 
considerable.  In  case  of  the  corn  crop  alone  it  has  been  estimated 
that  a  yearl}'-  loss  of  20  per  cent  of  the  crop,  or  $20,000,000,  is  caused 
thereby,  and  in  the  other  cereal  crops  the  loss  is  even  greater.  It 
should  be  mentioned  in  closing  this  discussion  that  the  rusts  and 
smuts  are  only  two  of  a  large  number  of  fungous  diseases  that  affect 
plants. 


CHAPTER  X 

PLANT   CLASSIFICATION 

I.   COMMON  METHODS  OF  CLASSIFICATION 

165.  Herbs,  shrubs,  and  trees.  —  One  way  of  classifying 
the  common  plants  with  which  we  are  most  familiar  is  that 
of  calling  them  either  herbs,  shrubs,  or  trees.  This  classifica- 


FIG.  78.  —  Base  of  one  of  the  giant  trees  of  California.  — (Tarr  and  McMurry.) 

tion  is  based  upon  the  general  similarity  in  size,  form,  and 
texture  of  the  plants  which  are  assigned  to  each  group.  Thus 
when  we  think  of  a  tree  we  have  in  mind  a  plant  which,  when 

154 


PLANT  CLASSIFICATION 


155 


1 


156 


PLANT  BIOLOGY 


mature,  is  of  large  size,  with  a  single  woody  trunk  and  branches. 
This  trunk  may  extend  up  nearly  to  the  top  of  the  tree,  as  in 
the  case  of  the  pines  and  spruces,  or  some  distance  above  the 
ground  the  trunk  may  divide  into  branches,  as  is  true  in  the 
elms  and  maples. 

A  shrub,  on  the  other  hand,  is  usually  of  smaller  size  even 
when  fully  grown  than  is  a  tree  ;  it  commonly  does  not  have  a 
single  trunk,  but  several  woody  stems  which  often  start  from 
the  ground  level,  as  in  the  lilac,  rose, 
and   witch   hazel.      Both   shrubs    and 
trees  are  alike  in  that  their  stems  and 
branches  do  not  die  down  to  the  ground 
at  the  end  of  the  season. 

An  herb,  as  the  term  is  used  in  plant 
biology,  is  a  plant  of  relatively  small 
size,  with  comparatively  little  woody 
material  in  its  stem,  which  dies  down  to 
the  ground  level  at  the  close  of  the 
season.  Such  are  beans,  corn,  and 
morning  glories.  The  roots  or  under- 
ground stems  of  some  herbs  —  for  ex- 
ample, dahlias,  carrots,  and  parsnips  — 

remain  alive  ready  for  growth  the  next  year.  These  facts 
suggest  another  method  of  classifying  plants,  namely,  as  : 


FIG.  80.  —  An  herb. 


166.  Annuals,  biennials,  and  perennials.  —  When  a  plant 
attains  its  maturity  in  one  season's  growth  and  then  dies,  as 
do  beans,  corn,  and  morning  glories,  such  a  plant  is  called  an 
annual.  Many  plants  which  have  fleshy  roots,  like  the  beet, 
carrot,  and  parsnip,  do  not  produce  flowers  and  seeds  until  the 
second  year.  During  the  first  season  after  the  seed  is  planted 
the  food  manufactured  in  the  leaves  passes  down  the  plant 
and  is  stored  beneath  the  ground.  At  the  end  of  the  season 


PLANT  CLASSIFICATION 


157 


the  stems  and  leaves  above  ground  die ;  but  if  this  root  re- 
mains in  the  ground  or  is  planted  the  next  season,  stems, 
leaves,  and  flowers  develop  rapidly,  and  finally  seeds  are 


FIG.  81.  —  Carrot.    A,  young  seedling;    B,  enlarging  root  early  in  season; 
C,  section  of  enlarged  root  late  in  season. 

formed,  the  food  stored  up  the  preceding  season  being  drawn 
upon  for  the  development  of  these  parts.  Plants  which  have 
a  life  history  like  this  and  which  live  for  two  years  only  are 


158 


PLANT  BIOLOGY 


called  biennials  (Latin,  bi  =  two -\-annus  =  year).  Perennials 
are  plants  that  live  year  after  year.  Hollyhocks  and  dahlias, 
for  instance,  store  food  in  fleshy  roots  year  after  year,  while 
the  parts  above  ground  die,  as  in  the  case  of  beets  and  carrots. 
Other  perennials,  like  trees  and  shrubs,  lose  only  their  leaves 
at  the  end  of  each  season. 

167.  Deciduous  and  evergreen  trees  and  shrubs.  —  Trees 
and  shrubs  may  be  classified  as  evergreen  or  deciduous.     Since 
the  leaves  of  pines,  spruces,  and  hemlocks  remain  green  and 
attached  to  the  stem  during  the  winter,  these  plants  are  known 
as  evergreens.     Certain  shrubs  (rhododendrons,  arbutus,  and 
wintergreen,    for    example)    also    keep    their   green   leaves 
throughout  the  winter,  and  so  in  a  sense  they  may  be  regarded 
as  evergreens.     Maples,  elms,  and  horse-chestnuts,  on  the 
other  hand,  shed  their  leaves  in  autumn;  they  are  therefore 
said  to  be  deciduous  (Latin,  de  =  hom-\-cadere=to  fall). 

168.  Field   work   on   plant    classification.     Optional.  —  No.    64. 

If  possible,  teachers  should  accompany  their  pupils  on  a  field  trip, 
point  out  and  name  the  plants  best  adapted  for  a  study  in  classifi- 
cation, using  perhaps  an  outline  like  the  following: 


NAME  OF 
PLANT 

HERB 

SHRUB 

TREE 

SIMPLE 
LEAVES 

COM- 
POUND 
LEAVES 

OPPO- 
SITE 
LEAVES 

ALTER- 
NATE 
LEAVES 

DECID- 
UOUS 

EVER- 
GREEN 

Rose  . 

X 

X 

X 

X 

II.    SCIENTIFIC  METHOD  OF  CLASSIFICATION 

169.  Scientific  classification  of  plants.  —  The  various 
methods  of  grouping  plants  that  we  have  thus  far  considered 
do  not  indicate  real  relationships  among  plants,  for  these 
schemes  call  attention  only  to  certain  superficial  resemblances 


PLANT  CLASSIFICATION  159 

and  differences  in  form,  or  size,  or  habit.  True  scientific 
classification  seeks  to  bring  together  into  a  given  group  all  the 
plants  that  are  closely  related  to  each  other;  that  is,  those 
which  are  probably  descended  from  common  ancestors.  In 
the  first  place,  all  plants  are  divided  into  two  great  groups 
known  as  seed-producing  plants,  and  spore-producing  plants. 
The  first  is  the  group  to  which  most  of  our  attention  has  thus 
far  been  given,  and  it  embraces  the  herbs,  shrubs,  and  trees, 
with  which  we  are  most  familiar.  We  should  bear  in  mind, 
however,  that  many  plants,  like  the  palm  and  rubber  plant, 
which  do  not  produce  flowers  in  our  climate,  develop  flowers, 
fruits,  and  seeds  when  they  are  growing  in  their  natural 
home.  Other  plants  with  inconspicuous  flowers  —  for  ex- 
ample, grasses,  elms,  and  pines  —  also  belong  to  this  great 
group  of  seed-producing  plants. 

Sub-kingdom  I,  Seed-producing  Plants  (Optional) 

170.  Gymnosperms   and    angiosperms.  —  Seed-producing  plants 
are  still  further  subdivided  into  two  groups.     The  first  group  includes 
all  plants  like  the  pines,  hemlocks,  and  spruces,  in  which  the  seeds  are 
not  produced  in  ovaries,  but  at  the  base  of  scale-like  leaves  which  are 
usually  grouped  together  to  form  cones;  hence  the  name  cone-bear- 
ing plants,  which  will  apply  to  the  common  forms.     The  whole  group 
is  known  as  gymnosperms  (from  Greek  meaning  naked  seeds). 

Plants  like  beans,  cucumbers,  and  pansies,  on  the  other  hand, 
develop  their  seeds  in  ovaries,  and  these  and  all  other  plants  of  this 
type  constitute  the  second  of  the  two  sub-divisions,  which  is  known 
as  the  angiosperms  (from  Greek  meaning  having  a  vessel  for  seeds). 

171.  Monocotyledons  and  dicotyledons.  —  Again,  the  seed-pro- 
ducing plants  may  be  classified  according  to  the  number  of  coty- 
ledons found  in  the  seed.     The  corn,  gladiolus,  and  lilies,  for  example, 
have  seeds  with  one  cotyledon,  and  hence  these  are  known  as  mono-' 
cotyledons     (Greek,  mono  =  one  4-  cotyledon).     Beans,    peas,    and 
maples,  on  the  other  hand,  have  two  cotyledons  and  are  therefore 


160 


PLANT  BIOLOGY 


called  dicotyledons  (Greek,  di  =  two  +  cotyledons).  There  are 
other  striking  characteristics  which  distinguish  these  two  groups  of 
angiosperms,  which  have  already  been  brought  out  in  our  laboratory 
work,  as  the  following  table  will  show: 


MONOCOTYLEDONS 
(Corn,  tulip,  gladiolus) 

DICOTYLEDONS 
(Bean,  horse-chestnut, 
pansy) 

Number  of  cotyledons 

one 

two 

Veining  of  leaves 

parallel 

netted 

Stem  structure 

woody  bundles  scat- 

bark, wood   in    dis- 

tered through  pith 

tinct  annual  rings, 

pith  in  center 

Number    of    stamens 

based    on    plan    of 

based  on  plan  of  five 

and  other  parts  of 

three      or     some 

or    some    number 

flower 

multiple  of  three 

other  than  three 

172.  Plant  families.  —  Continuing  our  classification  of  the  angio- 
sperm  group  still  further,  we  find  that  the  dicotyledons  are  sub- 
divided into  over  one  hundred  and  sixty  so-called  plant  families, 
some  of  which  are  the  violet  family,  the  buttercup  family,  the  rose 
family,  and  the  pulse  family.     This  grouping  into  families  is  based 
largely  upon  flower  structure,  and  so  it  sometimes   happens   that 
an  herb  and  a  tree  belong  to  the  same  family.     For  example,  the 
pea,  bean,  and  the  locust  tree  all  belong  to  the  pulse  family,  since 
they  have  flowers  closely  resembling  each  other. 

173.  Plant  genus.  —  Again,  each  of  the  160  or  more  families 
is  made  up  of  a  varying  number  of  more  closely  related  plant  groups, 
each  of  which  is  known  as  a  genus.     The  rose  family,  for  example, 
has  fourteen  genera,  some  of  which  are  the  pear  genus,  the  rose  genus, 
and  the  cherry  genus. 


174.    Plant  species.  —  Once  more,  each  genus  consists  of  a  vary- 
ing number  of  species,  the  members  of  which  resemble  each  other 


PLANT  CLASSIFICATION 


161 


very  closely.  The  pear  genus  consists  of  the  pear  species,  the  apple 
species,  and  the  crab  apple  species.  Species,  again,  may  be  still 
further  subdivided  into  varieties,  in  which  the  plants  are  more  closely 
related  (e.g.  Baldwin  and  Greening  varieties  among  apples) .  And 
finally  a  species  (or  variety)  is  made  up  of  individual  plants,  that 
resemble  each  other  in  all  essential  respects. 


Sub-kingdom  II,  Spore-producing  Plants  (Optional) 


A.   Ferns 


176.  The  fern  plant.  — 
We  turn  now  from  a  dis- 
cussion of  seed-bearing 
plants  to  a  consideration 
of  those  plants  which 
never  produce  flowers  or 
seeds.  As  a  representa- 
tive of  the  highest  group 
of  plants  without  seeds, 
we  will  study  the  ferns. 
The  majority  of  ferns 
grow  in  damp,  shady 
places,  and  among  the 
common  kinds  we  may 
name  the  brake,  the 
maiden-hair,  and  the  rock 
fern.  In  any  one  of  these 
ferns  the  parts  above 
ground  which  are  true 
leaves  are  known  as 
fronds.  The  main  axis 
of  each  frond  runs 
throughout  the  leaf,  and 
to  each  side  are  attached 
the  leaflets,  which  may  or 


FIG.  82.  —  Fern  plant  (Aspidium),  showing 
roots,  rhizome,  and  frond  :  A,  'section  of 
fruit  dot  (sorus) ,  showing  spore  cases,  some 
of  which  are  ejecting  their  spores  ;  B,  por- 
tion of  a  leaflet,  showing  unripe  fruit  dots  ; 
C,  portion  of  a  leaflet,  showing  ripe  fruit 
dots.  —  (Strasburger.) 


162 


PLANT  BIOLOGY 


may  not  be  still  further  subdivided.     Hence,  a  fern  leaf  is  usually 
compound,  and  is  strikingly  graceful  in  its  appearance. 

Beneath  the  ground  the  fronds  grow  from  a  horizontal  stem  called 
the  rhizome,  which  is  more  or  less  enlarged  for  food  storage,  depend- 
ing on  the  kind  of  fern.  To  this  rhi- 
zome are  attached  the  roots  by  which 
the  plant  is  supplied  with  soil-water. 
The  fern  plant,  therefore,  like  seed- 
bearing  plants,  has  all  three  kinds  of 
nutritive  organs  (roots,  stem,  and  leaves), 
and  carries  on  carbohydrate  manufacture 
in  the  green  fronds,  storing  away  the 
food  in  the  rhizome,  since  the  leaves  die 
to  the  ground  each  year.  The  follow- 
ing spring  the  tiny  leaves  push  up 
through  the  ground  from  the  under- 
ground stem,  unrolling  and  spreading 

their  leaflets  from  the  base  to  the  tip. 
FIG.  83.  —  Development  of 
fern  plant. 

A,  a  germinating  fern  spore ; 
B,  a  later  stage  in  germina- 
tion ;  C,  a  full-grown  pro- 
thallus, showing  rhizoids, 
antheridia  (or  spermaries, 

:variea™  B?g."i?on°cf  amined  with  a  microscope,  M  found  to 

antheridia  (or  spermary) ;  consist  of  several  smaller  objects  known 

E,  a  sperm  cell;  F,  a  section  as  spore-cases.     (B,C,  Fig.  82.)     When 

of    archegonia   (or    ovary)  .,                                                             ., 

containing   an  egg-cell  ;  G,  these  tmy  sPore  cases  are  nPe>  they  °Pen» 

young  fern  plant  develop-  often  with  considerable  force,  and  eject  a 

ing  from   a   fertilized   egg-  powder)  each  particle  of  which  is  called 

a  spore.     (Fig.  82,  A.)     Each  spore  con- 
sists of  a  single  cell. 


176.  Fern  spores.  —  On  the  under 
surface  of  some  of  the  leaflets  of  the 
ferns  named  above  are  little  dots  which 
are  often  brown.  These  are  known  as 
fruit-dots  (son).  Each  fruit  dot,  if  ex- 


cell in  an  ovary,  still  at- 
tached to  the  heart-shaped 
prothallus.  —  (Parker.) 


177.  Fern  prothallus.  —  When  the  spores  fall  to  the  ground  and 
conditions  are  favorable,  they  start  to  germinate,  and  each  finally 
produces  a  small  green,  heart-shaped  plant  known  as  a  prothallus 
(Fig.  83,  C).  The  prothallus,  though  tiny,  consists  of  a  great 


PLANT  CLASSIFICATION  163 

number  of  cells,  some  of  which  form  tiny  outgrowths  from  the  under 
surface  like  root-hairs  (called  rhizoids),  which  anchor  the  prothallus 
to  the  soil  and  aid  in  securing  food  materials. 

On  the  under  surface  likewise  of  each  prothallus,  in  the  region 
of  the  rhizoids,  are  minute  organs,  circular  in  appearance,  known  as 
antheridia  (spermaries),  in  which  are  produced  a  large  number  of 
sperm-cells  (Fig.  83,  D,  E).  At  a  little  distance  from  the  antheridia, 
near  the  notch  in  the  prothallus,  are  found  other  somewhat  elon- 
gated bodies  called  archegonia  (ovaries).  In  each  of  these  there  is 
developed  a  special  cell  known  as  the  egg-cell  (Fig.  83,  F). 

178.  Fertilization  of  the  egg-cells.  —  When  the  sperm-cells  are 
ripe,  the  antheridia  or  spermaries  are  ruptured,  and  the  sperm- 
cells  make  their  way  by  a  curious  twisting  motion  toward  the  open- 
ings on  the  archegonia.    A  single  sperm-cell  moves  down  the  tube 
of  each  archegonium,  and  penetrates  the  egg-cell,  and  the  two  nuclei 
unite  in  the  process  of  fertilization.     (See  91.)     From  the  fertilized 
egg-cell  develops  a  fern  plant  composed  of  many  cells  of  various 
kinds,  which  are  all  derived  from  the  fertilized  egg-cell. 

179.  Alternation  of  generations.  —  Thus  we  see  that  in  the  life- 
history  of  the  fern  plant  we  have  two  distinct  generations.     The 
first  is  the  ordinary  fern  plant,  which  is  familiar  to  all,  and  which  is 
known  as  the  asexual  generation  or  spore  generation,  because  the  spores 
formed  on  the  fronds  produce  the  next  generation   (prothallus) 
without  fertilization  or  the  union  of  two  kinds  of  cells.     The  second 
generation,  the  prothallus,  is  the  sexual  generation,  because,  as  we 
have  seen,  it  can  only  produce  a  fern  plant  from  the  fertilized  egg- 
cell.     In  plants  like  the  fern,  in  which  an  individual  (fern)  produces 
another  plant  (prothallus)  unlike  itself,  and  this  in  turn  gives  rise 
to  a  plant  like  the  original  (fern),  we  have  so-called  alternation  of 
generations. 

180.  Suggestions    for    the   study   of    the    fern.  —  No.   65.     If 
this  topic  is  suggested  for  study,  pupils  should  be  encouraged  to 
collect  their  own  material,  noting  the  surroundings  or  habitat  of  each 
kind  of  fern.     They  should  describe  the  location,  form,  and  color 
of  each  of  the  nutritive  organs,  and  of  the  fruit  dots,  and  draw  the 


164  PLANT  BIOLOGY 

entire  fern.  Each  student  should  study  a  prothallus  with  a  hand 
magnifier,  making  an  enlarged  drawing  of  the  same  to  show  its 
form  and  the  position  and  shape  of  the  rhizoids,  antheridia,  and  arche- 
gonia.  A  demonstration  of  the  steps  in  the  life  history  may  well 
be  shown  from  charts. 

B.   Mosses 

181.  The  moss  plant.  —  A  second   group  of   flowerless   plants 
includes  the  mosses.     In  general,  mosses  are  smaller  plants  than  the 
ferns,  but  like  them  are  usually  found  in  damp,  shady  places.     If 
one  examines  a  moss  plant  when  it  is  "  in  fruit,"  a  slender  stem  will 
be  seen  projecting  from  the  leafy  part  below.     At  the  upper  end 
of  this  slender  stem,  a  covered  cup-like  structure  is  evident  (Fig. 
84,  A,k).    This  cup,  or  capsule  as  it  is  called,  is  filled  with  tiny  dust- 
like  particles,  which  when  examined  with  a  compound  microscope 
prove  to  be  cells.     They  are  called  spores.     The  spores  are  repro- 
ductive bodies  similar  to  those  produced  in  the  spore  cases  of  ferns. 

182.  The  moss  protonema.  —  When  these   bodies  are  ripe,  the 
capsule  opens  and  discharges  some  of  the  spores,  which  fall  to  the 
ground  and  soon  begin  to  grow,  forming  at  first  an  elongated  cell 
(Fig.  84,  H)  which  later  divides,  giving  rise  to  two  cells.    This 
process  continues  until  a  slender,  green,  thread-like  mass  is  formed, 
with  many  branches.     This  thread-like  mass  is  called  the  protonema 
(Fig.  84,  G).     Some  of  the  branches  produce  buds  which  finally 
grow  into  the  leafy  structure  which  we  know  as  the  moss  plant 
(Fig.  84,  B,  A). 

183.  The  sexual  generation  of  the  moss.  — -  At  the  top  of  some 
moss  plants  at  certain  seasons  of  the  year,  in  the  midst  of  the  rosette 
of  green  moss  leaves,  may  be  found  tiny  flask-shaped  organs,  the 
archegonia  (ovaries)  (Fig.  84,  F).    At  the  base  of  each  of  these 
organs  is  produced  an  egg-cell.     Sometimes  in  the  same  moss  plant, 
and  sometimes  in  another,  are  to  be  found  club-shaped  organs  called 
antheridia  (spermaries)    (Fig.  84,  E).     In  the  antheridia  are  pro- 
duced sperm-cells   (Fig.  84,   D).     At  the  proper  time  the  sperm- 
cells  make  their  way  into  the  archegonia,  and  when  a  sperm-cell 


PLANT  CLASSIFICATION 


165 


reaches  an  egg-cell  they  fuse,  the  two  nuclei  unite,  and  a  fertilized 
egg-cell  is  formed.    This  fertilized  egg,  by  the  process  of  growth  and 


FIG.  84.  —  Development  of  a  moss  plant. 

A,  moss  plant  with  spore  case  (k)  having  a  lid  (c)  ;  z,  rhizoids ;  B,  young 
moss  plant ;  C,  enlarged  view  of  spore  ca'se,  with  lid  (c)  detached  ;  D, 
single  sperm-cell ;  E,  sperm ary  with  escaping  sperms  ;  F,  ovary  with 
dividing  egg-cell  (o)  ;  G,  branching  protonema  ;  H,  spore  germinating  to 
form  protonema. 

cell  division  (Fig.  84;  F,  o),  finally  forms  the  slender  stalk  with  the 
capsule  and  spores  at  the  end  of  it  like  that  referred  to  in  181 
(Fig.  84,  A,  C). 


166  PLANT  BIOLOGY 

184.  Alternation  of  generations  in  the  moss.  —  The  protonema 
and  the  leafy  shoots  with  their  antheridia  and  archegonia  are  known 
as  the  sexual  generation  because  it  is  this  plant  that  produces  eggs 
and  sperm- cells  which  must  unite  before  the  egg  can  develop  into 
the  spore-bearing  plant.  The  slender  stalk  with  the  capsule  at  the 
end  which  is  produced  by  the  fertilized  egg-cell  is  called  the  asexual 
generation,  since  the  spore-bearing  plant  can  reproduce  without  the 
union  of  two  kinds  of  cells.  The  spore-bearing  plant  is  dependent 
on  the  leafy  plant  for  all  its  food.  In  the  fern,  on  the  other  hand,  it 
is  evident  that  the  spore-bearing  plant  and  the  plant  producing 
eggs  and  sperms  are  entirely  independent  plants.  In  both  of  these 
groups  of  seedless  plants,  however,  there  is  an  alternation  of  genera- 
tions. 

186.  Suggestions  for  the  study  of  mosses.  —  No.  66.  The  teacher 
should  secure  plenty  of  material  for  the  demonstration  both  of 
the  plants  with  spore  cases  and  if  possible  the  plants  with  arche- 
gonia and  antheridia.  On  account  of  its  size  the  pigeon  wheat 
moss  is  desirable.  The  material  may  be  collected  and  dried,  since 
both  generations  are  not  likely  to  be  obtained  at  the  same  time  of 
year.  If  spore  cases  are  on  hand,  the  work  might  then  be  done  when 
the  sexual  plants  can  be  secured  in  a  fresh  condition.  The  pupil 
should  describe  and  draw  the  leafy  moss  plant.  The  location  of 
archegonia  and  antheridia  should  be  stated.  Then  the  spore-bear- 
ing plant  should  be  described,  together  with  the  relation  to  the  sexual 
plant  which  produced  it,  and  the  spore  case  opened  to  show  the  spores. 
The  two  plants  should  then  be  drawn  and  labeled. 

C.   Algce 

186.  Spirogyra.  —  Any  one  who  has  ever  been  in  parts  of  the 
country  where  ponds  or  very  slowly  moving  bodies  of  water  abound 
must  have  noticed  either  at  the  bottom  or  on  the  surface  of  the  water 
a  green,  slimy  mass.  It  is  so  frequently  found  on  the  surface  that  it 
is  called  "  pond  scum."  If  one  examines  a  small  portion  of  this  mass 
even  with  the  naked  eye,  one  will  see  that  it  consists  of  a  great  num- 
ber of  interlacing  threads.  When  looked  at  with  the  compound 


PLANT  CLASSIFICATION 


167 


microscope  each  of  these  threads  is  seen  to  be  a  series  of  cells  joined 
end  to  end.  All  the  cells  are  practically  the  same  in  shape  and 
structure,  however,  so  that  a  study  of  one  will  make  clear  the  struc- 
ture of  all. 

Inclosing  each  cell  there  is  a  thin  cell  wall.  The  first  structures 
one  is  likely  to  notice  within  the  cell  are  the  chlorophyll  bodies. 
In  the  pond  scum  known  as  Spirogyra  the  chlorophyll  is  arranged 
in  spiral  bands,  and  it  is  this  which  has  given  the  plant  its  name 
(Fig.  85,  B) .  In  other  forms  the  chlorophyll  is  differently  arranged, 


—  chlorophyll  band 


—  nucleus 


—  chlorophyll  band 


FIG.  85.  —  Spirogyra.  —  (Strasburger.) 
A,  two  conjugating  threads  of  Spirogyra  ;  B,  single  cell  of  Spirogyra. 

sometimes  in  star-shaped  masses,  one  in  each  half  of  the  cell,  and 
sometimes  diffused  throughout  the  cell.  If  a  little  iodine  is  added 
to  the  specimen  when  it  is  being  examined  under  the  microscope, 
a  nucleus  may  be  distinguished  near  the  center  of  each  cell  (Fig.  85, 
B).  In  the  cell-body  and  nucleus  the  protoplasm  appears  as  a 
clear  and  almost  transparent  mass. 


168  PLANT  BIOLOGY 

The  thread  or  filament  continues  to  increase  in  length  by  the 
growth  and  division  of  certain  individual  cells  that  compose  it. 
At  the  close  of  the  season  most  of  the  filaments  perish,  but  some  of 
them  undergo  peculiar  changes.  The  bands  of  chlorophyll  lose  their 
definiteness,  the  protoplasm  becomes  massed,  tiny  outgrowths  from 
the  sides  of  the  cells  occur,  and  ,these  continue  to  extend  till  they 
meet  similar  outgrowths  from  a  neighboring  filament  (Fig.  85,  A). 
These  outgrowths  unite,  and  thus  a  tube  from  one  cell  to  the  other 
is  formed.  The  contents  of  one  cell  pass  through  to  another,  and 
the  two  masses  fuse.  A  thick  wall  forms  about  the  united  mass  and 
the  old  cell  walls  decay  and  fall  away,  leaving  these  thick-walled 
zygospores  on  the  bottom  of  the  pond.  In  the  spring  the  protoplasm 
within  each  of  these  zygospores  begins  to  grow,  breaks  through  the 
thick  wall,  and  proceeds  to  form  a  new  filament  by  cell  division. 
The  formation  of  the  zygospores  is  known  as  conjugation;  it  is  a 
kind  of  sexual  reproduction,  though  the  two  cells  taking  part  in  the 
process  are  the  same  in  appearance. 

If  one  observes  pond  scum  on  a  sunny  day,  bubbles  will  be  seen 
escaping  from  the  mass.  A  test  of  this  gas  proves  it  to  be  oxygen, 
and  as  we  should  expect,  it  occurs  in  connection  with  the  process  of 
carbohydrate  manufacture  the  same  as  in  other  green  plants.  In 
fact  it  has  been  proved  that  these  simple  plants  manufacture  foods, 
digest,  assimilate,  respire,  and  reproduce  as  do  the  higher  plants 
we  have  studied.  The  differences,  then,  between  a  simple  plant 
like  Spirogyra  and  a  bean  plant  or  an  oak  tree  are  mainly  those  of 
structure  and  adaptations  for  the  performance  of  functions  which 
are  largely  common  to  both.  Indeed,  it  is  evident  that  every  cell 
of  the  Spirogyra  is  in  contact  with  the  water,  from  which  all  the  sub- 
stances needed  are  obtained  by  absorption.  Hence,  any  special 
adaptations  for  securing  food  materials  or  of  giving  off  wastes,  such 
as  are  found  in  higher  plants,  are  unnecessary. 

187.  Suggestions  for  the  study  of  Spirogyra.  —  No.  67.  It  is 
desirable  that  pupils  should  see  the  "  pond  scum  "  in  its  habitat, 
even  if  they  do  not  collect  material  for  work.  The  escape  of  bubbles 
may  be  noticed  at  this  time  or  in  the  laboratory.  The  mass  should  be 
described  as  to  color  and  "  feel/'  and  the  fine  threads  noted  by 


PLANT  CLASSIFICATION  169 

floating  the  mass  in  a  saucer  of  water.  A  filament  should  then  be 
studied  under  the  microscope,  and  the  parts  of  a  single  cell  described, 
and  several  cells  should  be  drawn.  If  fresh  zygospore  material  can 
be  obtained,  this  should  also  be  studied,  and  the  parts  described 
above  noted  and  drawn ;  otherwise  charts  or  pictures  may  be  used. 

188.  Pleurococcus  and  other  algae.  —  Another  and  still  simpler 
form  of  plant  life  is  known  as  Pleurococcus.     It  may  be  readily 
obtained  from  the  trunks  on  the  north  side  of 

large  trees.  It  appears  as  a  very  thin  green  layer 
closely  adhering  to  the  bark.  If  a  little  of  this 
material  is  scraped  off  and  placed  under  the 

compound  microscope,  it  will  be  found  that  it  is    , 

„       ,  »,.          .       ,  FIG.  86.  —  Pleuro- 

made  up  of  a  large  number  of  tiny  circular  green       coccus.  —  (Sedg- 

cells  which  adhere  to  each   other  more  or  less,      wick    and   Wil- 
since  in  the  process  of  reproduction  one  cell      son') 
divides  to  form  two,  each  of  which  is  considered  to  be  an  individual 
plant.     Thus  the  whole  mass  is  made  up  of  a  large  number  of 
one-celled  plants. 

The  Spirogyra  and  Pleurococcus  are  only  two  of  a  large  number 
of  simple  plants  known  as  algae.  They  differ  widely  in  form,  but 
none  of  them  develop  roots,  stems,  or  leaves.  Among  the  most 
common  algae  are  the  marine  forms  known  as  sea  weeds,  of  which 
there  are  many  kinds. 

189.  Suggestions  for  the  study  of  Pleurococcus.  —  No.  68.     As 
indicated  above,  material  for  the  study  of  Pleurococcus  may  be 
easily  obtained  by  removing  pieces  of  bark  from  trees  having  a  con- 
siderable quantity  of  this  plant  on  their  surface.     If  collected  in  a 
dry  season,  the  bark  should  be  placed  under  a  bell-jar  with  sufficient 
water  to  make  the  air  moist,  and  allowed  to  stand  for  several  days. 
The  place  in  which  the  Pleurococcus  is  found  should  be  described, 
and  also  the  appearance  of  a  mass  of  the  plants.     Single  cells  should 
then  be  studied  under  the  high  power  of  the  compound  microscope, 
and  the  cell  and  its  contents  described  and  drawn. 

D.   Fungi.     (See  Chapter  IX,  147-166.) 


170  PLANT  BIOLOGY 

III.  SUMMARY  OF  A  CLASSIFICATION  OF  THE  PLANT 
KINGDOM 

Division  I  —  Spore-producing  plants. 
Sub-division  1  —  Fungi      (including     bacteria,     yeast,     molds, 

mushrooms,  rusts,  smuts). 
Sub-division  2  —  Algce  (including  Spirogyra,  Pleurococcus,  and 

sea  weeds). 

Sub-division  3  —  Mosses  and  their  relatives. 
Sub-division  4  —  Ferns  and  their  relatives. 

Division  II  —  Seed-producing  plants. 

Sub-division  1  — •  Gymnosperms  (including  pines,   spruces,   hem- 
locks). 
Sub-division  2  —  Angiosperms,  composed  of  : 

Class  I  —  Monocotyledons  (e.g.  corn,  lilies,  gladiolus). 

Class  II  —  Dicotyledons  —  composed  of  160  or  more  families, 

one  of  which  is 

Rose  family  —  composed  of  14  genera,  one  of  which  is  the 
Pear  genus  —  composed  of  3  species,  one  of  which  is  the  — 
Apple   species,  of   which  there  are  many  varieties,  e.g. 
Baldwin,  Greening,  etc. 


APPENDIX   I 

LABORATORY  EQUIPMENT 

The  laboratory.  —  It  is  very  desirable  that  a  definite  room  or 
rooms  be  set  apart  for  work  in  biology,  since  at  least  a  minimum 
equipment  is  essential,  and  this  cannot  be  transferred  from  room 
to  room  without  considerable  loss  of  efficiency.  While  it  is  desirable 
to  have  tables  or  at  least  flat-topped  desks  of  good  size,  satisfactory 


FRONT    ELEYATTDM. 


END   ELEVATION- 


o 


TOP. 
FIG.  87.  —  Plans  for  a  laboratory  table. 

laboratory  work  can  be  done  in  an  ordinary  class  room  if  it  is  well 
lighted.  The  laboratory  should  be  supplied  with  a  demonstration 
table  and  gas  connection  if  possible,  with  sink  and  running  water, 
and  a  broad  shelf  should  be  placed  in  front  of  the  windows  for  sup- 
porting growing  plants  and  aquaria,  and  for  use  in  demonstrations 
with  the  compound  microscope.  Ample  closet  room  should  be  pro- 
vided in  which  to  store  apparatus  and  supplies,  so  that  they  may  be 
kept  free  from  dust. 

171 


172  PLANT  BIOLOGY 

In  case  it  is  possible  to  equip  a  room  with  laboratory  tables  the 
following  type  is  suggested.  In  the  first  place  the  laboratory  tables 
should  be  firmly  fixed  to  the  floor,  and  arranged  so  that  the  light 
comes  from  the  left  side,  and  if  possible  also  from  the  back  of  the 
room.  The  desk  tops  should  be  30  inches  from  the  floor  and  20 
inches  wide,  and  should  be  made  of  maple  or  other  hard  wood.  The 
length  of  each  table  will  of  course  depend  upon  the  dimensions  of 
the  room,  but  if  possible  no  more  than  three  pupils  should  be  pro- 
vided for  at  a  single  table.  Each  student  should  have  at  least 
30  inches  of  the  table  space.  (Fig.  87.) 

"  The  finish  of  the  laboratory  table  tops  is  a  matter  of  importance, 
since  it  must  be  such  as  to  protect  the  wood  from  damage,  and  keep 
it  clean  and  smooth.  Many  prefer  a  black  finish,  to  obtain  which  the 
following  method  gives  good  results. 

"  Make  up  solutions : 

(1)  Copper  sulphate  (CuS04)       .     .     .  625  grams 
Potassium  chlorate  (KC10  )  .     .     .  625  grams 
Water  to  make 5  liters 

(2)  Anilin  oil 300  grams 

Hydrochloric  acid  (HC1)    .     .     ,    .  450  grams 

Water  to  make 2500  liters 

"  Apply  solution  (1),  followed  immediately  by  (2)  several  times, 
until  the  wood  becomes  a  dark  green,  allowing  the  applications  to 
dry  each  time.  The  darker  the  tone  reached,  the  better.  The 
wood  must  then  be  washed  thoroughly  with  soap  and  hot  water 
applied  with  a  brush.  This  is  necessary  in  order  to  remove  the  super- 
fluous salts.  The  table  is  finished  with  oil  and  will  then  be  dead 
black."1 

The  advantages  of  the  dull  black  finish  are  these:  (1)  there  is 
little  reflection  of  light  from  this  kind  of  surface  into  the  eyes  of  the 
pupils;  (2)  the  black  surface  furnishes  an  admirable  background 
for  many  objects  of  study ;  and  (3)  the  tops  are  not  injured  by  water, 
acids,  or  other  chemicals. 

Experience  has  shown  that  unless  the  laboratory  must  be  used 

1  From  Lloyd  and  Bigelow's  "The  Teaching  of  Biology." 


APPENDIX  I  173 

as  an  assembly  room  for  a  division  at  the  beginning  and  close  of 
school,  drawers  and  shelves  beneath  the  desk  are  of  little  real  use, 
and  often  become  mere  receptacles  for  laboratory  de*bris,  unless 
they  are  provided  with  locks.  It  is  usually  far  safer  and  more  satis- 
factory to  collect  drawings,  magnifiers,  pencils,  etc.,  at  the  close 
of  the  period,  and  to  distribute  materials  as  they  are  needed  during 
the  next  period.  If  this  work  is  properly  systematized  and  the 
assistance  of  pupils  is  made  use  of,  very  little  of  the  laboratory 
time  is  lost  in  this  way. 

Seats  fixed  to  the  floor,  likewise,  are  of  great  advantage.  The 
authors  have  found  that  the  best  seat  for  this  purpose  is  the  Chandler 
chair,  which  is  furnished  by  the  American  Seating  Company, 
19  West  18th  St.,  New  York  City.  It  has  a  strong  iron  base,  which 
can  be  screwed  to  the  floor,  and  the  chair  seat  turns  on  ball-bear- 
ings through  an  arc  of  180  degrees.  The  price  of  the  chair  is  $2. 

Apparatus  and  chemicals.  —  The  following  lists  of  apparatus 
and  chemicals  are  suggested  as  a  minimum  equipment  for  a  class 
of  24.  Most  of  the  items  can  be  purchased  from  any  one  of  the  fol- 
lowing dealers : 

Bausch  and  Lomb  Optical  Co.,  Rochester,  New  York. 
Kny-Scheerer  Co.,  404  West  27th  St.,  New  York  City. 
O.  T.  Louis,  59  Fifth  Avenue,  New  York  City. 

QUANTITY  APPARATUS  AND  GLASSWARE  ESTIMATED  PRICE 

1        Compound  microscope,  with  |-  and  £-inch  objec- 
tives, double  nose-piece,    1  inch    eye-piece,  and 

revolving  disk-diaphragm $30.00 

24       Magnifiers,  doublets,  1^-inch  focus 16.20 

1        Harvard  trip-scale  balance        6.00 

12        Evaporating  dishes,  3  inches  diameter  ......  1.50 

1  2-quart  agate  double  boiler 1.50 

2  Alcohol  lamps  or        \ .50 

2  Bunsen  burners  (if  gas  is  available) .40 

3  ft.  Rubber  tubing  (heavy)  to  fit  Bunsen  burners     .     .  .60 
144       Slides,  plain,  1X3  inches .80 


174  PLANT  BIOLOGY 

1  oz .  Cover  glasses  (round) $   .70 

12        Sloyd  knives 2.25 

24  Forceps  (heavy) 5.00 

12        Dissecting  scissors 2.25 

50        Handles  (adjustable)  for  dissecting  needles    ...  2.00 

100        Needles  for  handles         25 

144        6-inch  test  tubes -.  1.50 

12        8-inch  test  tubes,  hard  glass 1.50 

2  Chemical  thermometers  (Fahrenheit  and  Centigrade 

scale  on  same) 2.00 

1        Lactometer        .50 

1  Radiometer 1.10 

2  Iron  ring-stands  (3  rings) 1.10 

2        Pieces  wire  gauze  (4X4  inches) .08 

2  Pieces  asbestos  (4X4  inches) .07 

6        Glass  stirring  rods .10 

25  ft.  Glass  tubing,  5  mm.  outside .30 

10  ft.  Rubber  tubing  to  fit  glass  tubing .70 

12        Thistle  tubes  (medium  size) 1.00 

12        Beakers,  150  to  250  cc 1.50 

3  Bell  jars  2  feet  high  and  10  inches  in  diameter   .     .  14.40 
3        Bell  jars  about  8  inches  high  and  10  inches  in  diam- 
eter        5.00 

1        Bell  jar,  open  top,  8  inches  high  and  8  inches  in 

diameter 2.00 

1  piece  Sheet  rubber  2  feet  square  (should  be  kept  in 

lightning  fruit  jar  when  not  in  use) 1.50 

24        Lightning  fruit  jars  (1  quart) 3.00 

6       Flasks,  250  cc 1.00 

36        Petri  dishes,  4  inches  in  diameter 6.00 

1        Cylindrical  graduate,  1000  cc 1.35 

1       Cylindrical  graduate,  100  cc .40 

6       Tall  glass  cylinders  (1000  cc.)       1.75 

1        Box  slide  labels 10 

1        Box  labels,  2x3  inches 18 

1        Steam  sterilizer,  copper  bottom,  18  inches  high  .     .  6.00 


APPENDIX  I  175 

50       8-ounce  wide-mouthed  bottles $2.20 

50       4-ounce  wide-mouthed  bottles «.  1.60 

24        200  cc.  narrow-mouthed  bottles  with  ground  glass 

stoppers 2.60 

100        Vials  with  corks,  3  inches  high,  1  inch  in  diameter    .  2.75 

100       Corks  to  fit  8-ounce  wide-mouthed  bottles     .     .     .  1.00 
100       Corks  to  fit  4-ounce  wide-mouthed  bottles     .     .    .-.,.        .75 

100       Corks  to  fit  6-inch  test  tubes V  .40. 

10        Rubber  stoppers  with  2  holes  to  fit  250-cc.  flasks  .     .  .45 

10  Rubber  stoppers  with  1  hole  to  fit  6-inch  test  tubes    .  .30 
2        Insect  spreading  boards ^1.00 

QUANTITY  CHARTS  AND  PREPARATIONS  ESTIMATED  PRICE 

11  Jung  plant  charts    (pansy,  horse-chestnut,   tulip, 

linden,  potato,  carrot,  pea,'  Spirogyra,  mold,  fern, 

moss) $13.20 

1        Teachers'  Botanical  Aid,  28  charts,  containing  300 
drawings  (Western  Publishing  House,  Chicago, 

111.) 12.50 

11  Jung  animal  charts  (fish  (external),  fish  (internal), 
frog,  Amoeba,  Paramecium,  crayfish,  bee,  but- 
terfly, cricket,  finch,  duck) 13.20 

4        Leuckhart  animal  charts  (grasshopper,  bee,  butter- 
fly, metamorphosis  of  frog) 8.00 

1        Model    of   heart    and  lungs    (dissectible),  natural 

size 12.75 

1        Model  of  digestive  system  on  panel,  natural  size      .  15.75 

1        Model  of  circulatory  system  on  panel,  natural  size    .  11.75 

1       Articulated  human  skeleton,  clutch  standard  .     .     .  35.00 

1        Life  history  of  butterfly 6.00 

1        Life  history  of  honey  bee 5.00 

1        Life  history  of  frog 5.00 

1        Life  history  of  fish 5.00 

1       Half  skeleton  of  fish  (glass  case) 3.00 

1       Half  skeleton  of  frog  (glass  case) 4.00 


176  PLANT  BIOLOGY 

8  Microscopical  slides  of  plant  tissue  (cross  section 
and  longitudinal  section  of  young  root,  cross 
section  and  longitudinal  section  of  stem  one  year 
old,  cross  section  of  hydrangea  leaf,  epidermis 
of  leaf,  separate  wood  cells,  ducts,  conjugating 

Spirogyra) $3.50 

5  Microscopical  slides  of  animals  (Amoeba,  Para- 
mecium,  frog's  blood,  human  blood,  mouth  parts 

of  bee) 3.00 

QUANTITY                  LIST  OF  CHEMICALS                  ESTIMATED  PRICE 

2  Ib.        Hydrochloric  acid $1.00 

1  Ib.        Nitric  acid .28 

1  Ib.        Ammonia .26 

1  oz.       Iodine 30 

5  oz.       Potassium  iodide     ...........  .90 

lib.         Ether 40 

1  Ib.        Caustic  soda       .30 

1             Small  tube  red  litmus  paper .08 

1             Small  tube  blue  litmus  paper .08 

1  gal.      95  per  cent  alcohol 3.50 

10  Ib.        40  per  cent  formalin 1.70 

8oz.        Glycerin -.  .25 

1  oz.        Pepsin       .30 

1  Ib.        Peptone 2.00 

1  oz.        Taka  diastase •  .  '  . .  1.70 

lib.        Salt .05 

1  oz.       Phosphate  of  lime .12 

1  Ib.        Grape  sugar        . .12 

£  Ib.        Cooking  soda .10 

1  Ib.        Copper  sulphate .35 

1  Ib.        Rochelle  salt 30 

1  jar       Beef  extract .75 

1  Ib.        Agar .90 

£  Ib.        Powdered  sulphur        07 

1  Ib.        Potassium  chlorate  .20 


APPENDIX  I  177 

£  lb.  Manganese  dioxid        $.35 

1  lb.  Granulated  zinc .25 

1  lb.  Absorbent  cotton .35 

6  Small  candles 10 

1  lb.  Marble  pieces ,     .  .10 

51b.  Plaster  of  Paris 10 

5  oz.  Potassium  cyanide .10 

1  oz.  Ferric  chloride .05 

1  lb.  Corn  starch .10 

^  lb.  Arrow  root  starch .15 

1  oz.  White  egg  albumen .12 

1  oz.  Powdered  carmine       .40 

1  oz.  Gluten  .15 


APPENDIX   II 

ORDER  OF  TOPICS 

The  following  order  of  topics,  with  time  assignment  for  each,  has 
been  found  by  the  authors  to  be  satisfactory : 

I.  Course  begun  in  September  and  completed  in  June. 

1.  ^"he  general  structure  of  plants  (organs  of  a  plant)       2  lessons 

2.  Reproduction  in  plants. 

a.  Structure  and  adaptations  of  flowers      ...     15  lessons 

b.  Structure  and  adaptations  of  fruits,  including 

fruit  and  seed  dispersal 5  lessons 

3.  Plant  propagation. 

a.  Seeds  and  their  development  into  plants    .     .      6  lessons 
6s  Conditions  essential  for  the  growth  of  plants   .       2  lessons 

4.  Cellular  structure  of  plants,  including  fertilization 

of  flowers 5  lessons 

5.  Composition  of  living  and  lifeless  things. 

a.  Elements,  compounds,  oxidation,  with  defini- 

tions       10  lessons 

b.  Composition  of  food  substances,  with  tests  for 

each       8  lessons 

c.  Manufacture  of  food  substances  by  plants  .     .  5  lessons 

6.  Osmosis  and  digestion 5  lessons 

7.  Adaptations  of  the  nutritive  organs  of  plants. 

a.  Structure  and  adaptations  of  roots    ....  5  lessons 

b.  Structure  and  adaptations  of  stems    ....  3  lessons 

c.  Structure  and  adaptations  of  leaves  ....  4  lessons 

8.  Respiration  and  the  production  of  energy  in  plants  4  lessons 

9.  Plants  in  their  relation  to  human  welfare. 

178 


APPENDIX  II  179 

a.  Some  uses  of  plants  to  man 3  lessons 

b.  Forests  and  forest  conservation 3  lessons 

10.  Single-celled  animals 5  lessons 

11.  Fish  (and  frog,  if  this  form  is  taught)     ....  14  lessons 

12.  The  general  structure  of  the  human  body  ...  3  lessons 

13.  Microorganisms  and  their  relation  to  human  wel- 

fare   10  lessons 

14.  Nutrients  and  their  uses 7  lessons 

15.  Stimulants,  narcotics,  and  poisons 10  lessons 

16.  Digestion  of  the  nutrients 7  lessons 

17.  Circulation  of  the  nutrients      .     .     .     .     .     .     .  6  lessons 

18.  Respiration  and  the  production  of  heat  and  power 

in  man 7  lessons 

19.  Additional  topics  in  hygiene 9  lessons 

20.  Birds 5  lessons 

21.  Insects 15  lessons 

II.  Course  begun  in  February  and  completed  in  January. 

1.  Composition  of  living  and  lifeless  things. 

a.  Elements,  compounds,  oxidation,  with  defini- 

tions       10  lessons 

b.  Composition  of  food  substances,  with  test  for 

each 8  lessons 

c.  Manufacture  of  food  substances  by  plants    .  5  lessons 

2.  General  structure  of  plants,  including  cellular 

structure 5  lessons 

3.  Osmosis  and  digestion 5  lessons 

4.  Adaptations  of  the  nutritive  organs  of  plants. 

a.  Structure  and  adaptations  of  roots  ....  5  lessons 

6.  Structure  and  adaptations  of  stems       ...  3  lessons 

c.   Structure  and  adaptations  of  leaves      ...  4  lessons 

5.  Respiration  and  the  production  of  energy  in  plants  4  lessons 

6.  Reproduction  in  plants. 

a.  Structure  and  adaptations  of  flowers    ...  15  lessons 

b.  Structure  and  adaptations  of  fruits,  including 

fruit  and  seed  dispersal 5  lessons 


180  PLANT  BIOLOGY 

7.  Plant  propagation. 

a.  Seeds  and  their  development  into  plants   .     .  6  lessons 

6.  Conditions  essential  for  the  growth  of  plants  .  2  lessons 

8.  Plants  in  their  relation  to  human  welfare. 

a.  Some  uses  of  plants  to  man 3  lessons 

6.  Forests  and  forest  conservation 3  lessons 

9.  Insects 15  lessons 

10.  Birds 5  lessons 

11.  Fish  (and  frog,  if  this  form  is  taught)  ....  14  lessons 

12.  Single-celled  animals 5  lessons 

13.  The  general  structure  of  the  human  body     .     .  3  lessons 

14.  Microorganisms  and  their  relation  to  human  wel- 

fare        10  lessons 

15.  Nutrients  and  their  uses 7  lessons 

16.  Stimulants,  narcotics,  and  poisons 10  lessons 

17.  Digestion  of  the  nutrients 7  lessons 

18.  Circulation  of  the  nutrients 6  lessons 

19.  Respiration  and  the  production  of  heat  and 

power  in  man 7  lessons 

20.  Additional  topics  in  hygiene    .         9  lessons 


APPENDIX  III 

BIOLOGY  NOTE-BOOKS 

Method  of  Recording  Laboratory  Observations.  —  In  preparing 
note-book  records  of  laboratory  observations  or  experiments, 
home  work,  or  field  trips,  the  teacher  should  insist,  so  far  as  possible, 
that  pupils  give  in  clear,  concise  English  a  complete  account  of  the 
work  that  has  been  done.  Students  should  be  careful  to  state  the 
purpose  of  the  experiment,  and  describe  the  preparation  of  the  ex- 
periment. He  should  indicate  whether  the  work  was  done  by  him- 
self or  by  some  one  else.  The  results  observed  should  be  sharply 
distinguished  from  the  conclusions  derived  from  observation. 
Pupils  might  well  use  as  paragraph  titles  the  section  titles  printed 
in  heavy  face  type  (e.g.  Carbon,  Oxygen,  etc.).  On  pp.  182-183  are 
two  accounts  of  the  same  experiments  that  were  photographed  from 
the  note-books  of  two  different  pupils.  The  method  of  writing  up 
an  experiment  shown  in  Fig.  88  is  suggested  for  accounts  that  are 
written  in  the  laboratory ;  that  in  Fig.  89,  for  accounts  written  at 
home. 

Drawings.  —  In  making  drawings  pupils  should  be  supplied  with 
sharp-pointed  pencils  that  are  relatively  hard.  Clear  outline  draw- 
ings should  be  insisted  upon,  and  shading  should  as  a  rule  not  be 
encouraged  (Figs.  90,  91).  The  general  title  of  the  sheet  of  drawings 
should  be  placed  at  the  top  of  the  sheet.  When  there  are  several 
drawings  on  the  same  sheet,  the  general  title  should  be  placed  at  the 
top,  and  the  special  title  of  each  should  be  written  just  below  the 
individual  drawing.  In  labeling,  the  dotted  leaders  may  run  in  any 
direction  (see  pp.  184-187),  but  they  should  not  cross  each  other. 
The  labels,  however,  should  all  be  written  parallel  to  the  top  margin 

181 


182  PLANT  BIOLOGY 

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FIG.  88.  —  Specimen  page  from  a  note-book. 


APPENDIX  III  183 


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FIG.  89.  —  Specimen  page  from  a  note-book. 


184 


PLANT  BIOLOGY 


FIG.  90.  —  Drawing  of  an  advanced  stage  of  the  corn  seedling. 


APPENDIX  III  185 

of  the  sheet.  If  the  drawings  are  made  on  separate  sheets  of  paper 
about  the  size  of  a  page  in  the  note-book,  the  sheets  may  be  col- 
lected, criticized,  and  rated,  and  then,  if  the  left-hand  margin  of  about 
an  inch  is  folded,  the  drawings  can  be  fastened  in  the  note-book  by 
pasting  this  narrow  flap. 

The  following  directions  for  guiding  pupils  in  the  preparation  of 
their  note-books  have  been  found  by  the  authors  to  be  of  great  assist- 
ance. 

1.  In  the  upper  right-hand  corner  of  the  outside  front  cover  of 

your  note-book  write  your  name,  division  (i.e.  grade  and 
section),  and  the  classroom  in  which  you  meet  at  9  A.M. 
thus: 

JOHN  S.  JONES,  1-8  (or  IA) 
Room  416 

Across  the  middle  of  the  front  cover  write  BIOLOGY  NOTE- 
BOOK. 

2.  Cover  your  note-book  with  manila  paper,  and  on  the  front 

cover  put  the  information  called  for  in  1  above.  Be 
sure  to  keep  your  note-book  covered. 

3.  Write  your  name,  division,  and  classroom  in  the  upper  right- 

hand  corner  of  the  first  page  of  your  note-book.  Leave 
the  rest  of  this  page  blank  for  the  teacher's  ratings  and 
comments. 

4.  Number  each  page  of  your  note-book. 

5.  On  each  of  the  pages  draw  a  vertical  line  about  an  inch  from 

the  left  margin.  Always  leave  this  marginal  space  for 
the  teacher's  comments. 

6.  Begin  each  new  subject  on  a  new  page,  writing  its  title  on  the 

first  line.  The  first  composition  or  notes  should  commence 
on  page  5,  the  preceding  pages  being  reserved  for  index. 

7.  Write  your  compositions  or  notes  in  ink  on  both  sides  of  the 

page. 

8.  Indent  about  an  inch  the  first  word  of  each  paragraph. 

All  other  lines  should  begin  at  the  left  margin  line.    It  is 


186  PLANT  BIOLOGY 

suggested  that  the  paragraph  titles  used  in  the  labora- 
tory studies  be  employed  and  that  they  be  underlined  (e.g. 
Parts  of  a  Leaf). 

9.  Make  sure  that  your  statements  in  each  paragraph  or  in 
your  notes  are  sufficiently  full  and  clear  to  be  readily 
intelligible  to  one  who  knows  nothing  of  the  subject. 

10.  In  your  compositions  or  notes  be  careful  to  make  clear  what 

you  yourself  did,  what  you  saw,  what  you  heard,  and  what 
you  read.  Accounts  of  experiments  may  often  be  written 
in  four  paragraphs  as  follows:  object  of  experiment; 
preparation  of  experiment ;  result  of  experiment ;  con- 
clusion from  experiment. 

11.  If,  on  account  of  absence,  it  is  necessary  that  work  be  copied, 

inclose  such  account  in  quotation  marks,  and  write  at 
the  end  of  such  quotation  the  name  of  the  pupil  from 
whom  the  account  was  copied. 

12.  Every  correction  indicated  by  the  teacher  should  be  made  by 

the  student  as  soon  as  the  note-book  is  returned. 

13.  Every  student  who  wishes  to  do  so  can  produce  a  first  class 

note-book,  neat  in  appearance,  and  at  least  relatively 
free  from  mistakes  in  spelling,  punctuation,  and  grammar. 

MARKS  USED  IN  THE  CORRECTION  OF  BIOLOGY  PAPERS 

cp  =  mistake  in  use  or  in  omission  of  capital  letter. 

cl   =  meaning  not  clear. 

gr  =  mistake  in  grammar. 

n    =  composition  is  lacking  in  neatness. 

II    =  error  in  paragraphing. 

p    =  mistake  in  punctuation. 

r    =  repetition  of  word  or  idea. 

sp  =  error  in  spelling. 

w  =  word  improperly  used. 

?   =  doubt  as  to  the  truth  of  the  statement. 

( )  =  words  in  parenthesis  are  to  be  crossed  out. 

A  =  some  omission. 


APPENDIX  III 


187 


FIG.  91.  —  Drawing  of  side  view  of  frog. 


APPENDIX   IV 

REVIEW  TOPICS  IN   PLANT  BIOLOGY 

You  should  be  prepared  to  give  a  good  oral  recitation  on  each  of  the 
following  topics.  If  you  are  not  sure  of  any  of  the  facts  called  for, 
write  down  the  topic  or  topics,  and  ask  your  teacher  at  the  beginning  of 
the  next  recitation  how  to  obtain  the  information. 

A.  COMPOSITION  OF  LIFELESS  AND  LIVING  THINGS. 

1.  Chemical  element:  definition ;  examples  with  symbols  of  each ; 

characteristics  of  each  (i.e.  whether  it  is  solid,  liquid,  or  gas ; 
color,  odor,  and  taste ;  ability  of  each  to  burn  or  to  cause 
burning). 

2.  Oxidation:    definition;    chemical  element  necessary;    com- 

pound formed  by  the  oxidation  of  elements ;  evidences  of 
oxidation. 

3.  Chemical  compound:    definition;    examples;    test  for  two  of 

them,  with  characteristics  of  each  (as  in  1  above). 

4.  Food  substances :  kinds ;   chemical  composition  of  each ;   test 

for  each ;  examples  of  foods  containing  each  in  abundance. 

5.  Manufacture  of  food  substances  by  plants : s  proofs  of  the  neces- 

sity of  sunlight,  chlorophyll,  and  carbon  dioxide  for  carbo- 
hydrate manufacture ;  proofs  of  the  excretion  of  oxygen  in 
carbohydrate  manufacture ;  manufacture  of  proteins. 

B.  GENERAL  STRUCTURE  OF  PLANTS. 

1.  Parts  of  a  plant ;  organs  and  functions. 

2.  Structure  of  plant  cells;  protoplasm;  assimilation,  growth, 

and  cell  division. 

188 


APPENDIX  IV  189 

C.  OSMOSIS  AND  DIGESTION. 

1.  Proofs  that  water  and  grape  sugar  will  pass  through  a  mem- 

brane ;  definition  and  law  of  osmosis. 

2.  Proofs  that  starch  and  protein  will  not  pass  through  a  mem- 

brane;  digestion  of  starch;   definition  of  digestion;   diges- 
tive ferments. 

D.  ADAPTATIONS  OF  THE  NUTRITIVE  ORGANS  OF  PLANTS. 

1.  Roots:  gross  structure;  structure  of  a  root-hair ;  functions  of 

roots  ;  adaptations  of  roots. 

2.  Stems :  gross  structure  of  a  woody  stem ;  functions  of  stems  ; 

adaptations  of  stems  ;  changes  in  stems  during  growth. 

3.  Leaves:    gross    and   microscopical   structure;    functions   of 

leaves ;  adaptations  of  leaves. 

E.  RESPIRATION  AND  THE  PRODUCTION  OF  ENERGY  IN  PLANTS. 

1.  Energy:   examples  in  plants;   proof  that  heat  energy  is  de- 

veloped in  growing  seedlings ;    transformations  of  energy; 
source  of  energy ;  oxidation  as  a  means  of  liberating  energy. 

2.  Respiration :  definition ;  proof  of  the  necessity  of  air  for  plants 

and  of  the  production  of  carbon  dioxide  by  plants. 

F.  REPRODUCTION  IN  SEED-PRODUCING  PLANTS. 

1.  Floral  envelopes:  names  of  the  parts  of  each  floral  envelope; 

position  and  general  description  of  the  floral  envelopes 
in  the  flowers  studied;  functions  of  each  of  the  floral 
envelopes. 

2.  Essential  organs:  name,  number,  position,  and  parts  of  each 

of  the  essential  organs;  general  description  and  func- 
tions of  the  parts  of  each  of  the  essential  organs. 

3.  Pollination. 

a.  Self-pollination :  definition ;  devices  to  prevent  it  in  flowers 

studied. 
6.  Cross-pollination :   definition ;   devices  to  make  it  possible 

in  flowers  studied ;   agencies  which  secure  cross-pollina- 


190  PLANT  BIOLOGY 

tion;  comparative  vigor  of  plants  from  seeds  resulting 
from  cross-pollinated  and  from  self-pollinated  flowers. 

4.  Fertilization. 

a.  Cellular  nature  of  pollen  and  ovules ;  germination  of  pollen 

grains. 

b.  Structure  of  ovule. 

c.  Process  of  fertilization ;  production  of  the  embryo. 

5.  Fruits. 

a.  Structure  of  each  of  fruits  studied;   definition  of  a  fruit; 

classification  of  fruits. 

b.  Necessity  for  seed-dispersal;   agencies  by  which  seed-dis- 

persal is  brought  about ;  adaptations  of  fruits  and  seeds 
to  secure  dispersal  by  each  of  these  agencies. 

c.  Adaptations  for  protecting  seeds  of  unripe  edible  fruits; 

adaptations  for  protecting  seeds  of  ripe  edible  fruits. 

G.  PLANT  PROPAGATION. 

1.  Bean  seed  and  its  development  into  a  seedling:    markings  on 

seed ;  their  cause  or  function ;  seed  covering ;  position 
and  kinds  of  stored  food;  description  of  parts  of  em- 
bryo ;  parts  of  the  plant  which  develop  from  the  parts 
of  the  embryo ;  breaking  of  seedling  through  the  soil. 

2.  (Optional.)     Corn  grain  and  its  development  into  a  seedling: 

description  of  the  parts  of  the  embryo;  position  and 
kinds  of  stored  food ;  breaking  of  seedling  through  the 
soil ;  various  parts  of  the  plant  which  develop  from  each 
of  the  parts  of  the  embryo. 

3.  Definitions:    seed,  seedling,  germination,  seed  coats,  micro- 

pyle,  hilum,  embryo,  cotyledon,  plumule,  hypocotyl, 
endosperm,  primary  and  secondary  roots. 

4.  Experiments  to  show  — 

a.  Function  of  endosperm  of  corn  grain. 
6.  (Optional.)     Relation  of  water  and  temperature  to  germi- 
nation. 

5.  (Optional.)     Other  methods  of  plant  propagation:  grafting; 

slips,  runners,  and  layers ;  tubers ;  bulbs. 


APPENDIX  IV  191 

6.  Conditions  essential  for  the  growth  of  plants :  five  essential  con- 

ditions ;  conditions  of  soil  favorable  for  growth ;  meth- 
ods of  soil  improvement. 

7.  (Optional.)     Struggle  for  existence  and  its  effects:    Variation 

among  plants;  numbers  of  seeds  produced  by  plants; 
struggle  for  existence  among  plants;  survival  of  the 
fittest. 

8.  (Optional.)     Improvement  of  plants  by  man:   artificial  selec- 

tion of  favorable  variations ;  artificial  crossing  of  related 
species ;  some  of  the  valuable  crops  of  New  York  State ; 
some  of  the  methods  of  increasing  crop  production. 

H.  PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE. 

1.  Some  uses  of  plants  to  man. 
a.  Uses  of  plants  for  food. 

6.  Uses  of  plants  for  flavoring  extracts,  beverages,  and  medi- 
cines. 
c.  Uses  of  plants  for  clothing. 

2.  Forests  and  forest  conservation.1 

a.  Definitions. 

(1)  A  forest  means  a  growth  of  trees  sufficiently  dense  to 

form  a  fairly  unbroken  canopy  of  trees.  A  forest 
has  a  population  of  animals  and  plants  peculiar 
to  itself,  a  soil  of  its  own  making,  and  a  climate 
different  from  that  of  the  open  country. 

(2)  "Forestry  is  the  preservation  of  forests  by  wise  use."  - 

ROOSEVELT. 

b.  Value  of  forests. 

(1)  ^Esthetic  value  —  beauty  of  form  and  color  of  forest 

trees. 

(2)  Value  in  affecting  drainage. 

(a)  By  retaining  water  in  the  soil  through  the  agency 
of  the  roots. 

1  The  authors  are  indebted  to  Miss  Kate  B.  Hixon,  of  the  Morris 
High  School,  New  York,  N.Y.,  for  the  review  topics  on  Forests  and 
Forest  Conservation. 


192  PLANT  BIOLOGY 

(b)  By  preventing  too  rapid  evaporation  from  the  soil, 

through  the  help  of  the  foliage. 

(c)  By  retarding  the  melting  of  snow,  thus  preventing 

freshets. 

(3)  Value  in  affecting  climate. 

(a)  By  bringing  moisture  into  the  air,  which  falls  as 

rain. 
(6)  By  setting  oxygen  free  into  the  air  in  the  process 

of  starch  making, 
(c)   By  acting  as  a  windbreak. 

(4)  Economic  value. 

(a)  As  a  source  of  lumber  and  fuel. 

(6)  As  a  source  of  food  (nuts,  maple  sugar,  etc.). 

(c)  As  a  source  of  industrial  raw  materials  (paper, 

tanning   materials,    wood   alcohol,    tar,    pitch, 

turpentine,  rosin,  fibers). 

c.  Dangers  to  forests. 

(1)  Fires.  (4)  Careless  lumbering. 

(2)  Insects.  (5)  Fungi  that  cause  disease. 

(3)  Grazing  of  cattle. 

d.  Results  of  deforestation. 

(1)  Main  cause  of  freshets,  which  cause  destruction  of 

property  and  loss  of  life ;  they  also  fill  up  navi- 
gable streams  with  soil  and  debris. 

(2)  Drouth,  with  the  consequent  lessening  of  water  power. 

(3)  Timber  famine,  especially  in  hard  woods. 

e.  Methods  used  by  the  Government  Bureau  of  Forestry  to 

preserve  forests. 

(1)  Allow  only  the  cutting  of  dead  or  mature  trees. 

(2)  Insist  that  each  tree  cut  be  replaced  by  another  of  the 

same  kind. 

(3)  Prevent  the  spread  of  fires. 

(4)  Destroy  insects  that  are  injurious  to  trees. 

(5)  Restrict  cattle  grazing  to  certain  seasons. 
3.  Fungi  and  their  relation  to  human  welfare. 

a.  Bacteria;   microscopical  appearance  and  size;   reproduc- 


APPENDIX  IV  193 

tion ;  necessary  conditions  for  growth ;  relation 
(1)  to  soil  fertility,  (2)  to  flavors  of  food,  (3)  to 
the  industries,  (4)  to  diseases. 

b.  (Optional.)     Yeast :    microscopical  appearance  and  size ; 

reproduction;  changes  caused  by  yeast;  uses 
of  yeast. 

c.  (Optional.)     Bread  mold;    structure;    reproduction  and 

life  history ;  nutrition  in  the  fungi. 

d.  (Optional.)     Other  fungi:  mushrooms,  rusts,  and  smuts; 

economic  importance. 

I.  PLANT  CLASSIFICATION. 

1.  Common  methods  of  classification. 

a.  Herbs,  shrubs,  and  trees :  define  each ;  give  examples. 

6.  Annuals,   biennials,  and  perennials;    define  each;    give 

examples, 
c.  Deciduous  and  evergreen  trees  and  shrubs:   define  each; 

give  examples. 

2.  (Optional.)     Scientific  method  of  classification. 

a.  Seed-producing  plants. 

(1)  Gymnospefms  and  angiosperms. 

(2)  Monocotyledons  and  dicotyledons. 

(3)  Plant  family,  genus,  species,  variety. 

b.  Spore-producing  plants. 

(1)  Ferns:   fern  plant;   spores;    prothallus;   fertilization 

of  the  egg-cells ;  alternation  of  generations. 

(2)  Mosses :  moss  plant ;  protonema ;   sexual  generation ; 

alternation  of  generations. 

(3)  Algae :   Spirogyra,  its  structure,  methods  of  reproduc- 

tion and  functions;  Pleurococcus  and  other 
algae. 

(4)  Fungi  (see  H,  3,  above). 

Note.     The  following  outlines  were  prepared  by  Miss  Martha 
F.  Goddard,  late  of  the  Morris   High  School,  New  York,  N.Y. 
They  furnish  an  admirable  review  of  the  most  important  nutritive 
o 


194  PLANT  BIOLOGY 

and  reproductive  functions  of  plants.  Pupils  might  either  copy 
the  whole  outline  into  their  note-books,  supplying  the  words  repre- 
sented by  the  figures,  or  make  a  list  of  the  words,  numbering  them 
to  correspond  to  the  figures  below. 

NUTRITION  IN  GREEN  PLANTS  THAT   PRODUCE   SEEDS 

Soil-water,  in  which  are  dissolved  compounds  that  contain  nitro- 
gen and  other  mineral  matters  needed  by  the  plant,  is  absorbed  by 
(1)  which  are  (2)  found  (3)  of  roots.  The  process  by  which  this  soil- 
water  enters  is  called  (4).  In  the  root-hair  the  membrane  is  the  (5). 
More  liquid  enters  the  root-hair  than  passes  out,  because  (6).  The 
substances  admitted  in  the  soil-water  are  regulated  by  the  action  of 
the  (7)  in  the  cell,  through  which  the  liquid  must  pass.  The  cell- 
sap  passes  from  one  cell  of  the  root  to  the  next,  until  it  reaches 
thick-walled  tubular  cells  called  (8),  which  form  part  of  the  (9)  of 
the  root,  stem,  and  leaf.  The  liquid  passes  up  through  these  un- 
til it  reaches  spaces  between  the  thin-walled  leaf-cells,  and  finally 
the  sap  gets  into  these  cells. 

A  gas  called  (10)  is  taken  in  through  epidermis  cells  of  the  leaf,  and 
through  openings  called  (11)  between  certain  cells  of  the  epidermis 
that  are  known  as  (12).  In  the  soft  cells  of  the  inside  of  the  leaf 
are  tiny  masses  of  protoplasm  which  contain  a  green  coloring  matter 
called  (13).  These  green  masses  of  protoplasm  are  called  (14). 
They  can  manufacture  starch  out  of  the  (15)  and  the  (16)  in  the 
presence  of  (17).  The  elements  in  C02  and  H20,  however,  are  not 
in  quite  the  right  proportions,  so  (18)  is  given  off  as  a  waste  product. 
The  soil- water  is  such  a  weak  solution  of  mineral  matter  that  not  all 
the  water  can  be  used  by  the  plant,  so  this  water  that  is  not  needed 
is  given  off  by  a  process  called  (19).  The  amount  of  water  thus  given 
off  is  regulated  by  the  action  of  the  (20)  that  surround  each  (21). 

During  the  night  the  starch  is  changed  to  (22)  by  a  process  known 
as  (23).  This  liquid  food  then  passes  down  through  the  (24)  of 
the  veins  and  bast  or  fibrous  bark  to  places  that  serve  for  storage 
or  to  growing  regions  where  it  is  used  to  make  a  substance  for  cell- 
wall  building  known  as  (25).  Some  of  the  sugar  is  made  by  the  pro- 


APPENDIX  IF  195 

toplasm  of  the  plant  to  unite  with  the  nitrogen  of  the  nitrates  and 
with  the  sulphur  and  phosphorus  of  other  mineral  matters  derived 
from  the  soil,  and  a  compound  is  formed  called  (26)  which  the  grow- 
ing regions  use  to  make  into  more  (27).  This  last  change  is  called 
assimilation. 

Some  of  the  proteids  may  also  be  stored  for  future  use.  Food 
may  be  stored  in  the  (28),  the  (29),  the  (30),  the  (31),  or  in  any  thin- 
walled  cells. 

OPTIONAL.    THE  LIFE-HISTORY  OF   A  SEED-PLANT 

See  note,  p.  193. 

The  mother-plant  produces  flowers  which  attract  insects  by  their 
(1)  or  by  their  (2).  These  animals  carry  (3)  on  their  hairy  bodies 
from  the  (4)  of  one  flower  to  the  (5)  of  another.  Here  nourished 
by  a  (6)  it  sends  out  a  tube  which  grows  down  through  (a)  the  (7), 
(6)  the  (8),  and  (c)  the  (9),  and  here  enters  a  tiny  opening  called  the 
(10)  in  the  (11).  There  a  nucleus  of  the  pollen  grain  (called  a  sperm 
nucleus)  unites  with  a  nucleus  of  the  egg-cell  in  the  ovule  during  the 
process  of  (12)  to  form  one  cell  (called  a  fertilized  egg-cell)  which 
now  develops  into  a  tiny  plant  known  as  the  (13)  of  the  seed.  This 
little  plant  has  (a)  a  minute  stem  called  the  (14),  (6)  one,  two,  or 
more  seed-leaves  known  as  (15),  and  (c)  usually  a  tiny  bud  called  the 
(16). 

The  mother-plant  feeds  this  embryo  until  it  has  grown  thus  far, 
and  also  stores  up  food  for  further  growth.  This  may  be  put  in  the 
cotyledons  as  in  the  (17)  seed,  or  it  may  be  packed  around  the 
embryo,  when  it  is  called  (18),  as  in  the  (19).  To  protect  the  embryo 
until  time  for  germination,  the  seed  has  one  or  more  outer  coverings 
known  as  (20) .  That  the  seed  may  be  carried  away  from  the  mother- 
plant,  and  so  have  better  opportunities  for  development,  the 
mother-plant  provides  the  fruit  or  the  seeds  (a)  with  (21)  or  (22)  so 
they  may  be  carried  by  the  wind,  or  (6)  with  (23)  so  they  may  cling  to 
the  wool  of  animals,  or  (c)  with  (24)  so  they  may  tempt  animals  to 
eat  them ;  in  the  last  case  (as  in  the  peach  or  cherry)  the  contents 
of  the  seed  are  protected  by  (25). 


196  PLANT  BIOLOGY 

When  the  seed  has  favorable  surroundings,  namely  (26),  (27), 
and  (28),  it  germinates.  If  it  has  one  cotyledon,  the  plant  is 
called  (29),  the  woody  bundles  in  its  stem  will  be  (30),  and  the 
veining  of  the  leaves  will  probably  be  (31).  If  two  cotyledons  are 
present  in  the  seed,  the  plant  is  called  (32),  the  woody  bundles  in 
its  stem  will  be  arranged  (33),  and  the  veining  of  the  leaves  will 
be  (34). 

The  principal  food  materials  stored  in  seeds  are  three  in  number, 
namely,  (a)  (35),  which  is  tested  by  (36) ;  (6)  (37),  tested  by  (38) ; 
and  (c)  (39),  tested  by  (40).  Sometimes  a  fourth  nutrient  (41)  is 
stored  in  other  parts  of  the  plant ;  its  presence  may  be  detected 
by  (42). 


APPENDIX   V 

LIST  OF  SUGGESTED  BOOKS  OF  REFERENCE  IN  BIOLOGY 

GENERAL  BIOLOGY 

1.  Cyclopedia  of  American  Agriculture.     Edited  by  L.  H.  Bailey. 

4  vols.  —  The  Macmillan  Co.,  N.  Y.  City.  $20  net. 
Vol.  I,  Farms;  Vol.  II,  Crops;  Vol.  Ill,  Animals;  Vol.  IV, 
The  Farm  and  the  Community.  We  do  not  hesitate  to  say 
that  Vols.  II  and  III  of  this  series  are  the  most  valuable 
books  of  reference  known  to  us  for  teachers  or  students  in  plant 
and  animal  biology.  Experts  on  the  many  subjects  treated 
have  epitomized  in  a  readable  form  a  vast  amount  of  informa- 
tion which  could  only  be  found  by  patient  search  through 
many  volumes.  If  schools  cannot  purchase  these  books, 
teachers  might  well  urge  that  they  be  put  on  the  shelves  of 
the  public  library,  for  all  four  volumes  will  be  found  of  great 
value  as  books  of  general  reference,  especially  in  rural  com- 
munities. 

2.  Nature  Study  and  Life,  by  Dr.  C.  F.  Hodge.  —  Ginn  and  Co. 

$1.20.  Contains  many  suggestions  for  the  teaching  of  both 
plant  and  animal  biology. 

3.  General  Biology,  by  Sedgwick  and  Wilson.  —  Henry  Holt  and 

Co.  $1.75.  While  mainly  devoted  to  a  consideration  of 
the  earthworm  and  the  fern  (both  optional  topics),  this 
book  will  give  teachers  a  clear  idea  of  the  biology  of  a  plant 
and  of  an  animal,  and  of  the  composition  and  character- 
istics of  protoplasm.  It  also  contains  an  admirable  account 
of  yeast,  bacteria,  Amoeba  and  Paramecium. 
197 


198  PLANT  BIOLOGY 

4.  Teaching  of    Biology,  by  Lloyd  and  Bigelow.  —  Longmans, 

Green  and  Co.  $1.50.  Deals  largely  with  methods  of 
teaching  nature  study,  botany,  zoology,  and  human  physi- 
ology. 

PLANT  BIOLOGY 

5.  Practical  Botany,  by  Bergen  and  Caldwell.  —  Ginn  and  Co. 

$1.30. 

6.  College  Botany,  by  G.  F.  Atkinson.  —  Henry  Holt  and  Co. 

$1.50. 

7.  Readers   in   Botany,   by  Jane   C.   Newell.  —  Ginn   and   Co. 

2  vols.     $.60  each. 

8.  How  to  know  the  Wild  Flowers,  by  Mrs.  William  Starr  Dana. 

-  The  Macmillan  Co.     $1 .50. 

9.  How   to   know   the   Fruits,  by   Maude  G.  Peterson.  —  The 

Macmillan  Co.     $1.50. 

10.  Tree  Book,  by  Julia  E.  Rogers.  —  Doubleday,  Page  and  Co. 

$4. 

11.  New  Creations  in  Plant  Life,  by  W.  S.  Harwood.  —  The  Mac- 

millan Co.     $1.75. 

12.  Bacteria,  Yeasts,  and  Moulds  in  the  Home,  by  H.  W.  Conn.  — 

Ginn  and  Co.     $1. 

13.  Farmers'  Bulletins,  which  can  be  obtained  free  by  applying  to 

the  U.  S.  Dept.  of  Agriculture,  Washington,  D.C.  The 
various  Bulletins  contain  many  important  facts  relating 
to  both  animals  and  plants. 

ANIMAL  BIOLOGY 

14.  Animal  Life,  by  Jordan  and  Kellogg.  —  Appleton.     $1.20. 

15.  General   Zoology,    by   Linville   and   Kelly.  —  Ginn   and   Co. 

$1.50. 

16.  American    Natural    History    (vertebrates    only),    by    W.    T. 

Hornaday.     $3.50. 

17.  Insect  Book,  by  L.  0.  Howard.  —  Doubleday,  Page  and  Co. 

$3. 


APPENDIX   V  199 

18.  Manual  of  Insects,  by  Comstock.  —  Comstock  Publishing  Co., 

Ithaca,  N.Y.    $3.75. 

19.  Economic  Entomology,  by  J.  B.  Smith.     Lippincott.     $2.50. 

20.  Birds  of  North-Eastern  United  States,  by  Frank  Chapman.  — 

Appleton.     $3. 

21.  Bird  Life  (with  colored  plates),  by  Frank  Chapman.  —  Apple- 

ton.     $2. 

22.  Relation  of  Birds  to  Man,  by  Weed  and  Dearborn.     Lippincott. 

$2.50. 

23.  Food  and  Game  Fishes,  by  Jordan  and  Everman.  —  Doubleday, 

Page  and  Co.     $4. 

24.  Farmers'  Bulletins  (see  13  above). 

25.  Story  of  the  Fishes,  by  J.  N.  Baskett.  —  Appleton.    $.65. 

HUMAN  BIOLOGY 

26.  The  Human  Mechanism,  by  Hough  and  Sedgwick.  —  Ginn  and 

Co.     $2.50. 

27.  General   Physiology,   by   W.    H.   Howell.     W.  B.    Saunders. 

$4. 

28.  Studies  in  Physiology,  by  James  E.  Peabody.  —  The   Mac- 

millan  Co.     $1.10. 

29.  Laboratory  Exercises  in  Anatomy  and  Physiology,  by  James  E. 

Peabody.     Henry  Holt  and  Co.     $.60. 

30.  Infection   and    Immunity,  by  George    M.    Sternberg. — Put- 

nams.    $1.75. 

31.  Pathogenic  Micro-organisms,  by  W.  H.  Park.  —  Lea  Brothers 

and  Co.     $3.75. 

32.  Walter  Reed  and  Yellow  Fever,  by  H.  A.  Kelly.  —  McClure, 

Phillips  and  Co.     $1.50. 

33.  The    Malaria    Mosquito,   by    B.    E.   Dahlgren.  —  American 

Museum  of  Natural  History.    $.15. 


INDEX 


Aerial  roots,  102. 

Ailanthus  fruit,  92. 

Air,  need  of,  for  growth,  67. 

relation  of,  to  soil,  111. 
Air  roots,  102. 
Air  spaces,  60,  62,  Fig.  22. 
Alcohol,  formed  by  yeast,  147. 
Algae,  166-169. 
Alternate  arrangement,  52. 
Alternation  of  generations,  in  fern, 
163. 

in  moss,  166. 
Angiosperms,  159,  170. 
Annual,  an,  156. 
Annual  rings,  47,  51,  Fig.  17. 
Annual  scars,  55. 
Anther,  71,  73,  81,  88,  Fig.  25. 
Antheridia,  of  fern,  162,  Fig.  83,  D. 

of  moss,  164. 

Apparatus,  price-list  of,  173-175. 
Apple,  fruit,  Figs.  37,  38. 

leaves,  Fig.  19. 
Archegonia  of  fern,  163,  Fig.  83,  F. 

of  moss,  164,  Fig.  84. 
Artificial  crossing  of  related  species, 

120. 

Artificial  selection,  119. 
Asexual  generation,  of  fern,  163. 

of  moss,  166. 
Asparagus,  127. 
Assimilation,  31. 

Bacillus   form   of   bacteria,   Fig.   71, 

B,  C,  D. 

Bacteria,  140-145,  Fig.  71. 
Bamboo,  49,  Fig.  18. 
Bark,  45. 
Bast,  46. 
Bean  fruit,  89. 
Bean  seed,  97-100. 
Bee,  Figs.  30,  31 


Beggar's  ticks,  93. 

Benzine  as  used  in  testing  for  fat,  20. 

Beverages,  128-130. 

Bidens,  93. 

Biennial,  158. 

Biology,  definition  of,  4. 

Blade  of  leaf,  55. 

Body,  cell-,  28,  29. 

Books,   list  suggested  for  reference, 

197-199. 

Botany,  definition  of,  4. 
Bread-making,  148. 
Bread  mold,  149-151. 
Breathing  in  plants  and  animals,  69. 
Budding  of  yeast,  146,  Fig.  74. 
Buds,  53. 

of  yeast,  146. 
Bud-scales,  53. 
Bud-scale  scars,  55. 
Bulbs,  108. 
Bumblebees,  81. 
Burbank,  Luther,  122. 
Burdock,  93. 
Burs,  93. 

Cabbage,  127. 

Calyx,  71,  79,  88. 

Cambium,  46,  51,  63. 

Camphor,  129.    ' 

Capsule  of  moss,  164. 

Carbohydrates,  meaning  of,  13,  14. 

composition,  13,  14. 

manufacture  of,  24,  60,  69. 
Carbon,  6. 
Carbon  dioxid,  7,  8. 

in  air,  11. 

necessary  for  starch  manufacture, 
23. 

formed  in  growing  plants,  68. 

formed  by  yeast,  147. 
Castor  bean  seedling,  Fig.  44. 


201 


202 


INDEX 


Cauliflower,  127. 

Cell-body,  28,  29. 

Cell  division,  30. 

Cell-nucleus,  28,  29. 

Cell-sap,  30. 

Cells  of  plants,  27,  29,  Figs.  6,  7. 

definition,  30. 

osmosis  in,  34. 
Cellulose,  29. 
Cell-wall,  28,  29. 
Central  cylinder  of  roots,  39. 
Charts,  price-list  of,  175-176. 
Chemicals,  price-list  of,  176-177. 
Cherries,  96. 
Chestnut,  fruits,  Fig.  39. 

leaf,  Fig.  20,  B. 
Chlorophyll,  23,  28,  51,  60,  62,  Fig. 

22. 

Chlorophyll  bands,  167,  Fig.  85. 
Chocolate,  129,  Fig.  63. 
Cider,  148. 
Cilia,  140,  Fig.  71. 
Cinchona,  129. 
Citranges,  122. 

Classification  of  plants,  154-170. 
Clay,  110. 
Coal,  133. 

Coal  period,  forests  of,  Fig.  65. 
Coccus  form  of  bacteria,  Fig.  71,  A. 
Cocklebur,  93. 
Cocoa,  129,  Fig.  63. 
Coffee,  129,  Fig.  61. 
Colony  of  bacteria,  142,  Fig.  71,  A. 
Compound,  definition  of,  12. 
Compound  leaf,  56. 
Conditions  essential  for  plant  growth, 

108-114. 

Conjugation  in  spirogyra,  168. 
Conservation  of  forests,  138. 
Consumption,  due  to  bacteria,  145. 
Corn,  cross-pollination,  85. 
Corn  grain,  95,  128. 
Corn  grains,  101. 

nutrients  stored  in,  104. 

use  of  endosperm  of,  104. 
Corn  production  in  U.  S.,  119. 
Corn  seedling,  100. 
Corn  stalk,  47,  49,  50. 
Corn  "tassels,"  87,  Fig.  33. 


Corn  ears,  88. 

silk,  88. 

Corolla,  71,  79,  88. 
Cortex  of  roots,  39. 
Cotton,  130-132. 
Cotyledon,  98,  101. 
Crops,  valuable,  of  N.  Y.  State,  122, 

Fig.  58. 
Crossing,  artificial,  of  related  species, 

120. 
Cross-pollination,  79. 

by  bumblebees,  81. 

in  pansy,  82-84. 

by  insects,  86. 

by  wind,  87. 
Cucumber  fruit,  90. 
Cultivation  of  soil,  113. 

Dairy  products  of  N.  Y.  State,  123. 
Dandelion  plant,  Fig.  55. 
Dangers  to  forests,  137. 
Darwin,  Charles,  82,  118,  Fig.  54. 
Deciduous  trees  and  shrubs,  158. 
Decomposition,    result   of    action   of 

bacteria,  140. 
Diastase,  36. 
Dicotyledons,  160,  170. 
Digestion,  definition  of,  37. 

of  starch,  37. 
Digestive  ferments,  38. 
Diphtheria,  due  to  bacteria,  145. 
Directions  for  note-books,  185-186. 
Disease-producing  bacteria,  145. 
Dispersal  of  seeds,  91. 
Distillation,  147. 
Distilled  liquors,  148. 
Division  of  cell,  30. 
Drainage,  111,  114. 
Drawings,  in  laboratory,    181,   Figs. 

90,  91. 
Drugs,  130. 
Dry  fruits,  96. 
Ducts,  45,  50,  62,  Fig.  14. 

Egg-cell,  77. 

Element,  definition  of,  12. 

Elm  fruit,  92. 

Elodea,  25,  28.  Fig.  5. 

Embryo,  77,  98,  Fig.  29. 


INDEX 


203 


Endosperm,  101. 

use  of,  104. 
Energy,  definition,  64. 

transformations  of,  65. 

liberation  of,  66,  67. 

source  of,  66. 
Epidermis,  of  root,  44,  62. 

of  stem,  51,  62. 

of  leaf,  56,  61,  62,  Figs.  21,  22. 
Equipment  of  laboratory,  171-177. 
Erosion,  as  result  of   destruction    of 

forests,  137. 

Essential  organs,  71,  73. 
Evergreen  trees  and  shrubs,  158. 
Excretion  of  water,  61. 
Existence,  struggle  for,  114-119,  Fig. 
53. 

Family,  plant,  160,  170. 
Fat,  composition  of,  14,  15. 

test  for,  19. 

Fehling's  solution,  preparation  of,  17. 
Fermentation,  148. 
Ferments,  digestive,  38. 
Ferns,  161-164,  Figs.  82,  83. 
Fertilization,  76,  77,  88. 

of  egg-cell  in  fern,  163. 
Fertilized  egg-cell,  77. 
Fertilizers,  114. 

Fiber-producing  plants,  130-132. 
Fibers,  47. 
Fibrous  bark,  46. 
Filament,  71,  73,  88,  Fig.  25. 
Fippin,  E.  O.,  123. 
Fire,  lanes,  139. 

wardens,  139. 
Flavoring  extracts,  128. 
Flavors  of  food,  145. 
Flax,  130. 

Fleshy  fruits,  93,  96. 
Floods,  prevention  of,  136. 
Floral  envelopes,  71,  72,  79,  88. 
Flowers,  70-88. 

tulip,  70-72. 

gladiolus,  72-74. 

pansy  79-82. 
Food  substances,  list  of  13. 

manufacture  by  plants,  22,  60. 

transfer  of,  50. 


Food  substances,  storage  of,  61. 

in  corn  grains,  104.     . 
Forest  conservation,  138. 
Forest  fires,  134,  137,  139. 
Forests,  dangers  to,  137. 
Fronds  of  ferns,  161. 
Frosts,  loss  of  crops  due  to,  117. 
Fruit,  definition  of,  94. 

hybrid,  122. 

stalk,  91,  92. 
Fruits,  89-96. 
Fuel,  133. 

Functions  of  organs,  27. 
Fungi,    relation    to    human    welfare, 

139-153. 

Fungous  diseases,  loss  of  crops  due 
to,  117. 

Garden,  tumbler,  102. 

glass-plate,  102. 
Generations,   alternation  of,  in  fern, 

163. 

Generative  nucleus,  77. 
Genus,  plant,  160,  170. 
Germination  of  pollen  grains,  76. 
Gladiolus,  72-74. 
Glass-plate  garden,  102. 
Goddard,  Miss  Martha  F.,  193. 
Grafting,  105-106. 
Grapes,  129. 
Grape  sugar,  composition  of,  14,  15. 

test  for,  16. 

osmosis  of,  33. 
Gravel,  110. 
Grazing  animals,  a  danger  to  young 

trees,  137. 

Growth  of  crystals,  2  (footnote). 
Growth  of  living  things,  2,  30. 
Growth  of  plants,  five  essential  con- 
ditions for,  108. 
Guard-cells  of  stoma,  58,  61,  62,  Fig. 

21. 
Gymnosperms,  159,  170. 

Harrow,  114,  Fig.  51. 

Hay  crop  of  N.  Y.  State,  122. 

Heat,  energy,  64. 

relation  of,  to  soil,  112. 
Hemp,  130,  145. 


204 


INDEX 


Herb,  156,  Fig.  80. 

High  school  education,  value  of,  124. 

Hilum,  97. 

Hixon,  Miss  Kate  B.,  191  (footnote). 

Horse-chestnut,  stem,  45,  52. 

leaves,  Fig.  20,  K. 
Human  welfare,  relation  of  plants  to, 

126-153. 
Humus,  111. 
Hybrid  fruits,  122. 
Hydrogen,  9. 
Hyphse  of  molds,  150. 
Hypocotyl,  98. 

Improvement  of  plants  by  man,  119- 

125,  Figs.  57,  59. 
Indigo,  preparation  of,  145. 
Insects,  a  danger  to  forests,  137. 

loss  of  crops  due  to,  117. 
Iodine  solution,  preparation,  15. 
Irrigation,  111. 

Jute,  145. 

Kerosene,  133. 

King,  Dr.  C.  A.,  102  (footnote). 

Kupfer,  Miss  Elsie  M.  (footnote),  27. 

Laboratory  equipment,  171-177. 

table,  171. 
Lateral  buds,  53. 
Layer,  106. 
Leaflets,  56. 
Leaf  scars,  53. 
Leaf-stalk,  55. 
Leaves,  arrangement  of,  52. 

Structure  of,  55. 
Lenticels,  51,  55,  62. 
Lettuce,  127. 

Life-history  of  a  seed-plant,  195. 
Lifeless  things,  characteristics  of,   1. 
Lilac  leaf,  Fig.  20,  A. 
Lime  water,  preparation  of,  5. 
Linden  fruit,  91. 
Linen,  preparation  of,  145. 
Living  things,  characteristics  of,  1. 
Lumber,  133. 

Lumbering,  wrong  method  of,  Fig.  67. 
right  method  of,  Fig.  68. 


Malt,  148. 

Mann,  Paul  B.,  66  (footnote). 

Maple,  fruit,  91. 

sugar,  136. 
Medicines,  129-130. 
Medullary  rays,  47,  50,  Fig.  17. 
Mesophyll,  57,  60. 
Micropyle,  76,  98,  Fig.  29. 
Milkweed  fruit  and  seeds,  92,  Fig.  36. 
Mineral  matter,  test  for,  20. 
Mixture,  definition  of,  12. 
Moisture,  relation  to  germination  and 

growth,  108-109. 
Mold,  bread,  149-151,  Fig.  75. 

vegetable,  111. 

Monocotyledons,  159,  160,  170. 
Mosses,  164-166,  Fig.  84. 

moss  plant,  164. 

protonema,  164. 
Mushrooms,  151,  Fig.  76. 

Nectar,  80. 

Nitric  acid,  test  for  protein,  18. 

Nitrogen,  11. 

Note-books  in  biology,  181-187. 

Nucleus,  28,  29. 

Nutrition,  in  fungi,  150. 

in  green  plants  that  produce  seeds, 

194. 
Nutritive  hyphse,  150. 

organs  of  plants,  39. 

Oak,  wood,  46. 

leaves,  Fig.  20,  C,  G. 

tree,  amount  of  evaporation   from 

136. 

Opium,  129. 

Opposite  arrangement,  52. 
Orange  crop,  120-122. 
Order  of  topics,  178-180. 
Organs,  of  a  plant,  27. 

nutritive,  39. 
Osmosis,  32-38. 

water,  33. 

of  grape  sugar,  33. 

in  living  cells,  34. 

of  starch,  35. 

definition  and  applications,  35. 

protein,  37. 


INDEX 


205 


Osmosis,  in  root-hairs,  44. 
Ovary,  72,  73,  81,  88. 
Ovules,  72,  74. 
Oxidation,  definition  of,  13. 

liberation  of  energy  by,  66. 

relation    of    oxygen    and    carbon 

dioxid  to,  67. 
Oxygen,  6. 

given  off  by  green  plants  in  sun- 
light, 25. 

supply  of,  for  animals,  25. 

necessity  of,  for  growth,  67. 

Palmately  compound,  56. 
Pansy,  79-82. 

Darwin's  experiments  with,  82-84. 
Parsnips,  127,  156. 
Peaches,  96,  128. 
Pea,  flower,  Fig.  35. 

fruit,  89,  Figs.  35,  43. 
Peppermint,  129. 
Perennials,  158. 
Petals,  71,  79,  88. 
Pinnately  compound,  56. 
Pistil,  71,  73,  81,  88,  Figs.  24,  28. 
Pistillate  flowers,  87,  Figs.  32,  B,  34. 
Pith,  46,  47,  63. 
Pith  rays,  47,  63. 
Placenta,  89. 
Plant,  family,  160,  170. 

genus,  160,  170. 

species,  161,  170. 

variety,  161,  170. 
Plants,  parts  of,  26-31. 

organs  and  functions,  27. 

microscopic  structure,  27. 

cells,  27. 

nutritive  organs,  39. 
Pleurococcus,  169,  Fig.  86. 
Plow,  113,  Fig.  50. 
Plumule,  98. 
Pollen,  71,  73,  Fig.  26. 
Pollen  tubes,  75,  Figs.  26,  27. 
Pollination,  74,  76,  88. 
Pond  scum,  166. 
Poppy,  129. 

Potato  crop  of  N.  Y.  State,  122. 
Potatoes,  107,  127,  Fig.  49. 
Preparations  for  laboratory,  175. 


Prevention  of  self-pollination,  84-85. 
Primary  root,  100. 
Protection  of  forests,  138-139. 
Protein,  use  of  term,  13  (footnote). 

composition  of,  14,  15. 

test  for,  18. 

manufacture  of,  24,  61. 

osmosis,  37. 

Prothallus  of  fern,  162,  Fig.  83. 
Protonema  of  moss,  164. 
Protoplasm,  30. 
Prudden,  Dr.  T.  M.,  142. 
Pumpkin,  cross-pollination,  85. 

Quartered  oak,  47. 
Quinine,  129. 

Radiometer,  66  (footnote). 
Rainfall,  regulation  of,  136. 
Raspberry  fruits,  Fig.  40. 
Reference  books,   list  of,   suggested, 

197-199. 
Reforesting,  138. 
Repair  of  living  things,  2. 
Reproduction,  of  living  things,  3. 

in  plants,  70-96. 

Reproductive  hyphse  of  molds,  150. 
Respiration,  definition,  68,  69. 
Review  topics  in  plant  biology,  188- 

196. 

Rhizoids  of  ferns,  163,  Fig.  83,  Y7. 
Rhizome  of  fern,  162,  Fig.  82. 
Rind,  47. 
Root-hairs,  40,  Figs.  11,  12,  13. 

osmosis  in,  44. 
Roots,  structure  of,  39-41. 

functions  of,  41-43. 

primary,  100. 

secondary,  100. 

aerial,  102. 
Root-tip,  40. 
Root-tubercles,  144,  Fig.  72. 

bacteria  in,  Fig.  73. 
Rotation  of  crops,  124. 
Runner,  106. 
Rusts,  152. 

Sand,  110. 
Sap,  of  cell,  30. 


206 


INDEX 


Sap,  path  through  roots,  42,  43. 

path  through  stem,  48,  49. 

path  through  leaves,  59. 
Schleiden  and  Schwann,  29. 
Science  and  its  subdivisions,  3. 
Scion,  105. 
Sea  weeds,  169. 
Secondary  root,  100. 
Seed-coat,  98. 
Seed-dispersal,  91-94. 
Seed-leaves,  98. 

Seedlings,  comparison  of,  103-104. 
Seed-producing  plants,  159—161. 
Seeds,  72,  74,  77,  97-105. 

numbers,  produced  by  plants,  115. 
Selection,  artificial,  119. 
Self-pollination,  79. 

prevention  of,  84-86. 
Sepals,  71,  79,  88. 
Sexual  generation,  in  fern,  163. 

in  moss,  164,  166. 
Sheath  leaf,  100. 
Shrub,  156,  Fig.  79. 
Sieve  tubes,  50,  62,  Fig.  16. 
Slip,  106. 

Smuts,  152-153,  Fig.  77. 
Soil,  110-114. 

moisture  of  111. 

air  in,  111. 

heat,  relation  of  soil  to,  112. 

cultivation  of,  113. 
Soil  water,  absorption  of,  41. 

transmission  of,  42,  48,  58. 
Sorus  of  fern,  162,  Fig.  82. 
Source  of  energy,  66. 
Species,  plant,  161,  170. 
Spermaries  of  fern,  163. 
Sperm-cells  of  fern,  163. 
Sperm  nucleus,  77,  Figs.  27,  28,  29. 
Spirillum  form  of  bacteria,  Fig.  71,  D, 
Spirogyra,  167,  Fig.  85. 
Spore-cases,  of  mold,  150. 

of  ferns,  162,  Figs.  82,  83. 
Spore    formation    in    bacteria,     143, 

Fig.  71,  D. 

Spore-producing  plants,  161-170. 
Spores,  of  mold,  150. 

of  ferns,  162,  Figs.  82,  83. 
Spur,  80. 


Squash,  cross-pollination,  86,  Fig.  32. 
Squash,  seedling,  Fig.  45. 
Stamens,  71,  72,  80,  88,  Fig.  24. 
Staminate  flowers,  87,  Figs.  32,  A,  33. 
Starch,  composition  of,  13,  15. 

test  for,  15. 

manufacture  in  sunlight,  22. 

manufacture  by  different  kinds  of 
leaves,  22  (footnote). 

manufacture  by  chlorophyll,  23. 

digestion  of,  36,  37. 
Stems,  structure,  45-48. 

functions  of,  48—51. 

changes  during  growth,  51. 
Stickers,  93. 

Stigma,  72,  73,  81,  88,  Fig.  25. 
Stipules,  56. 
Stock,  105. 

Stoma,  58,  60,  61,  62,  Figs.  21,  22. 
Stone  fruits,  96. 
Storage  of  foods,  61. 
Story  of  bacteria,  142  (footnote). 
Strawberry,  flower,  Fig.  41. 

fruit,  Fig.  42. 

plant,  Fig.  48. 
Struggle  for  existence  among  plants, 

114-119,  Fig.  53. 
Style,  73,  81,  88. 
Sugar  cane,  127. 
Sun,  as  source  of  energy,  66. 
Sunlight,  necessary  for  starch  manu- 
facture, 22. 
Survival  of  the  fittest,  118-119,  Figs. 

53,  55. 
Sweet  potato,  127,  Fig.  60. 

Tea,  129,  Fig.  62. 
Temperature,  of  soil,  112. 

relation   of,    to    germination    and 

growth,  109. 
Terminal  bud,  53. 
Toadstools,  151. 
Tokay  grape  fruit,  90. 
Tomato  fruit,  90. 
Topics,  order  of,  178-180. 
Transfer  of  food  materials,  50,  62. 
Transformations  of  energy,  65. 
Tree,  154,  Figs.  78,  79. 
Tubers,  107. 


INDEX 


207 


Tufted  fruits  or  seeds,  92. 

Tulip,  flower,  70-72. 

Tumbler  garden,  102. 

Typhoid  fever  due  to  bacteria,  145. 

Uses  of  plants,  127-132. 
of  forests,  132-137. 

Variation  among  plants,  114,  Fig.  52. 

Variety,  plant,  161,  170. 

Vegetable  crop  of  N.  Y.  State,  122. 

Vegetable  mold,  111. 

Veins  of  leaf,  55. 

Vinegar,  preparation  of,  145. 

Wall,  of  cell,  28,  29. 

of  ovary,  72,  73. 

Water,  composition  and  preparation, 
10. 

test  for,  20. 


Water,  osmosis  of,  33. 

given  off  from  leaves,  59. 
Webber,  Dr.  H.  J.,  120-122. 
Wheat,  128. 

seedling,  Fig.  46. 
Window  box,  102. 
Wine,  129,  148. 
Winged  fruits,  91. 
Wood,  46. 

Wood-cells,  43,  49,  63. 
Woody  bundles,  47,  50,  Fig.  15. 

Yeast,  146-149,  Fig.  74. 
reproduction  of,  146. 
buds,  146. 

changes  caused  by,  147. 
148. 


Zoology,  definition,  4. 
Zygospores  of  spirogyra,  168 


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